Just make a minimal install of OS X in a small partition in your HD, or much better yet, in an external drive. Use it for Mac-only maintenance, disaster recovery, and stuff like EFI updates.

Of course, as Ash-Fox said, you should research the EFI update very carefully before installing it to make sure Linux compatibility isn't affected.

It seems you don't completely understand what an app bundle in OS X is. Yes, it is a directory where all the files that comprise an app are packaged up nice and neat.

But that directory is treated by the Finder in a special way: from the point of view of an end user, it is just a file. He double clicks on it, and the app launches. He drags a document icon on top of it, and the document opens in the app. He can move it around, move it to another disk or to another Mac, etc., and it consistently behaves like a single file and retains its functionality. Only when he right-clicks on it and chooses "Show Package Contents" is its true identity as a neatly organized folder revealed.

In fact, app bundles aren't the only kind of packages (i.e., directories that present themselves as files) in OS X. There are many others. For example, some apps like Apple's Keynote save documents as packages. From the point of view of most users, a Keynote file is pretty much like a PowerPoint file, except for the app that opens it. A slightly more advanced user knows that he can right click on the Keynote file, search for the graphs he included in the presentation, and replace those files (PNG, JPEG, PDF, whatever) with updated versions that reflect updated data... and the presentation gets updated without even opening Keynote.

Maybe. In that case, just buy it from the Apple store:
http://store.apple.com/us/prod...

Mmmm... Ok, but you are exaggerating in this statement:

Of all Mac Pro models only the earliest four don't run OS X 10.10 Yosemite. But all four of them can be upgraded to 10.7.5, as you can verify by clicking on their links in that page.

I find it odd that an owner of such a machine wouldn't know that.

Searching again for a suitable replacement for Time Machine I found Back In Time, which seems to have the same functionality as tym but with a reasonable GUI. That's great and helps alleviate the pain for a non-technical user. But it is still based on rsync --link-dest and as I said before that has very big technical disadvantages when compared to Time Machine.

No, not by a long shot. They both allow you to take snapshots of your files/drive, but that's where the similarity ends.
Time Machine's implementation, both from the technical standpoint and from the user experience one, sets it apart from VSS. A consequence of that is that Time Machine is a system that even clueless end users can (and do!) take advantage of.

For a good summary of Time Machine's implementation see the excellent Ars Technica review of OS X 10.5 Leopard by John Siracusa.

Quite frankly the only backup+versioning system that I can recall that has similar functionality to Time Machine is tym, a rather complex bash script that leverages the --link-dest option of rsync. I use it to back up other Unix-like systems, as well as data on OS X machines for which I don't have administrative access.

But quite frankly it has many technical disadvantages, and furthermore it is not something that I would expect an end user to be able to configure and use. Of course you can roll out a much simpler script like this, but then again you are losing even more functionality and still suffer from the technical drawbacks without really improving the usability for non-technical users.

Nope. As SuperKendall said in a separate reply, regular users can't modify the backups and administrators (sudoers) need to authenticate to modify them. (And yes, I verified it before posting this).

The malware would therefore need to escalate the privileges in order to encrypt the backups, making it far more challenging.

I can assure you: leave a used condom on top of your valuables and no one who enters that hotel room will touch them.

Racism aside, sexual intercourse with small flying mammals should be actively discouraged, regardless of age.

Then let's go for Spring break!

You will have to patch your system manually.

True. You can nevertheless patch older versions of OS X manually.

Update: I just learned that there is indeed a way to tag files in Linux (well, in KDE apps at least). In its current incarnation it is called Baloo, and it is now implemented pretty much like tags are implemented in OS X, that is by incorporating the tags in an extended attribute for the file.

Unfortunately when I google "baloo kde" I do see quite a bit of pages asking or showing how to disable Baloo. I guess it's still in its infancy and still suffers from performance issues. (Baloo actually does much more than tagging, it is the whole file indexing system, so it is more akin to Spotlight on the Mac side.)

That is fantastic! Thank you very much for the info!

For others that may be interested in file tagging in Linux, it seems there are two systems: the old one called Nepomuk and its replacement Baloo.

Nepomuk uses a database that needs to be running permanently which associates tags and files. That approach has too many drawbacks, and quite frankly would be an unsatisfactory substitute for OS X's tagging.

Baloo, on the other hand, does things the right way, by incorporating the tags into an extended attribute for the file. That is exactly the way it's done in OS X, and it works awesomely provided that you have a good indexing system that indexes those extended attributes like Spotlight does. (Close-to-immediate searches are fundamental for the success of a system-wide tagging system.)

Thanks again for the info!

I am aware that the original poster wants to use Linux and may be talked into using Windows but probably not into buying a Mac. But since other people will have the same question and some of them may be Mac users, here it goes:

Many responders have already suggested creating ingenious folder structures that will help you keep a basic level of organization to the photo collection. Use any of those systems, and augment it by making use of OS X's extremely useful tagging feature.

Furthermore, there are many applications, such as the ones made by Ironic Software, that allow you to search, organize, and work with your files in very powerful ways using those tags. Since the tagging system is common to all of them you are not tied to any particular application.

The only downside of this is that you do become dependent on OS X at least until other systems implement tagging.