A /30 in fact provides "4 addresses" and is the standard point-to-point IP subnetwork as it allows for two real hosts (plus network address and network broadcast address, both traditionally unusable). Magic number method is a quick way to not get tripped up on this sort of math.

A subnet's address size is inversely proportional (but without constant ratio) to the percentage of "lost" addresses.

/30 - 4 Addresses - 2 Usable - 50% Lost
/29 - 8 Addresses - 6 Usable - 25% Lost
/28 - 16 Addresses - 14 Usable - 12.5% Lost

-Weaver

I am the author of Portable Thunderbird with Enigmail / GPG (PTEG). I have been following Mobility Email and have had correspondence with its author (Shane). I took a look a the latest release (Beta 4).

It is composed mainly of JH latest PTB release (based on Deer Park) and the launcher that JH, myself, and many others have been tweaking for the past year to get it to what it is today. Mobility Email relies on those two pieces and adds a few additional extensions (RTFA to find out which ones), "pretty" documentation, and a lot of marketing speak.

That being said I think it is a good thing for several reasons. The most important of which is that it attempts to de-geekify (not a word) the whole signing/encrypting/portable mail thing. Many layman are thrown off by the geek nature of the sites that JH and I have for our work. Shane's work makes it easier (partly in part because it is pretty) for the layman to get into it.

Sure it is a rip-off in some sense. The technical work has nearly all been done. It is a repackaging of what is out there. The same could be said for what I put together off of JH's PTB. Although I did a chunk of programming and tweaked the launcher heavily, with some changes being added back into JH's vanilla launcher. Shane does give nods to the community, you just have to search for it.

From TFA:

What is included with Mobility Email?

Mobility Email is based on Portable Thunderbird with Enigmail/GPG by John Urbanek.

The specific software included in the distribution is:

        * Thunderbird 1.5 Beta 2 (with additions by John T. Haller).
        * Enigmail 0.93.0 by the Enigmail Team.
        * GNU Privacy Guard (GnuPG) 1.4.2 (Win32) by GNU.
        * WebMail 0.7.0 by the WebMail Team.
        * Hotmail 0.8.0 for WebMail by the Webmail Team.
        * Yahoo! 0.5.1 for WebMail by the Webmail Team.
        * MailDotCom 0.4.1 for Webmail by the WebMail Team.
        * Lycos 0.6.1 for Webmail by the WebMail Team.
        * Talkback 1.4.1 by the Mozilla Team.

The only thing I was a little surprised at was that he didn't include the source to the launcher, which is what really does all the magic. JH and I have been including it since the beginning. Maybe Shane is trying to hide as much of the technical fluff as possible from the end user. Either way, I think what he is doing is a step in the right direction.

On another note, I'll be releasing a version of PTEG based off of Deer Park not too long from now. Many have been asking for the feature to encrypt the profile directory as well. I am eventually planning on rewriting the launcher in C (or something more powerful than NSIS) and utilizing some of the symmetric encryption capabilities of GnuPG to encrypt the profile folder.

-John