Corporate Desktop:
Here are some things you should keep in mind. Since 2006, among Linux users, the Open Directory model where OpenLDAP runs a directory service, Samba 3.x runs a PDC, and Heimdal Kerberos runs the KDC, and FreeRadius runs RADIUS has been extremely popular. Open Directory (OpenLDAP+Samba+Heimdal Kerberos) was a definite step above the Sun Yellow Pages+NFS, or early NT4 Domains created by Samba 2.2, and it ran like a well oiled machine. Certain distributors supported it well. Mandriva and Suse being model citizens, while Ubuntu not so much. Ubuntu and Debian did a horrible job with Samba, LDAP and Kerberos. But Samba, LDAP, and Kerberos as Open Directory aren't MS Active Directory. That cost the Linux world many casualties. For the longest time, AD Dominated.
I recently tried Samba 4.0 Alpha 15 and was able to create a mostly functional Windows 2008 R2 Style Forest. I ran into problems incorporating Open Directory applications and schemas used to OpenLDAP's model, but I am certain those can be resolved. Samba 4.0 will have all the features of Open Directory and all of Active Directory's forms combined. It will likely replace OpenLDAP and Heimdal Kerberos because it is so much easier to manage just one application that does all three, and is completely compatible with its predecessors in the Unix world's feature sets.
In the future, I can see Samba 4 becoming the predominant Server for both Windows AD Clients, and Unix Clients running applications like NFS and AFS, FreeRadius, PostFix, eGroupware, and Zimbra. At the same time offering AD support to AD Clients. If you think it can't happen, just remember that Windows 7 has special code in it's registry to allow Samba 3 Domains to authenticate with Windows 7 clients, and even though Samba 3 style domains are still in some sense NT4 Domains, while NT4 itself is completely incompatible with Windows 7.
Samba 4 can devour the AD market inside out.
Home Desktop
What really matters here are games. Linux desktop needs to be able to run games of all platforms, for Windows, this of course means Wine. Wine again, is in a position to become more compatible with Windows than real Windows. There are now, a few applications that will run on Wine but not Modern Windows. This is mostly Games from the 9x era. But as time moves on, we may see more XP games that work on Wine that won't work on Windows.
Android support is another issue. A market for Android phones is growing, and Linux needs some sort of API translation layer to run Android games on PCs.
Desktop Interface:
Another thing is this: The constant desktop shifting and changing has to stop. someone really needs to back the Trinity Desktop Environment. Both KDE and Gnome now take away system resources from video cards to make the desktop look and interact more wth the user. This needs to stop. These effects slow the machine down, they slow games down, they slow EVERYTHING down. What I want is an interface that runs what I tell it to run. I would be extremely angry if my game was slowed down by KDE compositing, Gnome effects, Compiz or Beyrl. They look cool, but, they are completely useless and take away from resources I need for other things.