Another solution to the problem of quotas occurred to me today: local quotas. Since the Windows workstation copies everything in the roaming profile from the server to the local machine at login, and uses that data as the user works, it actually makes a lot more sense for quotas to happen on the local workstation itself. This way, rather then becoming aware of quotas at logout only, the workstation is always aware of the state of the user's home account quota, because that quota exists on the volume where the profile actively lives.
Doing this also prevents the error message at logout due to exceeding a server-side quota. In this new, local-quota scenario, the user is alerted the instant he exceeds his quota and can rectify the situation immediately. But if he doesn't, no problem. As long as the local quota and the server-side quota match, he'll never run into the problem of being unable to save his settings to the server, since he'll never be able to exceed his quota anyway.
It turns out that, unlike on Mac OS X, setting quotas for NTFS volumes is incredibly easy. In fact, it's a simple matter of viewing the properties of the drive on which you want to set quotas.
Here, go to the Quotas tab and click "Enable quota management" and "Deny disk space to users exceeding quota limit," set the limits, and you're basically done. The administrator will have no quotas, and any new user will have the quotas specified in this panel. You may, however, want to set certain users (particularly other admin or local users) to have larger quotas, or none at all. Again, exceptionally easy: Click that badly named, but ever-useful little "Quota Entries..." button and you'll get a list of local users and their quotas.
Here, you can set quotas for specific users. Initially, you'll only see local users. But after any network user logs in, you'll also see them listed as well.
The more I think about it, the more I like the idea of local Windows quotas. Using them does away with all the problems mentioned in earlier posts, and may help with a lot of the quota-related problems users have with our current, Windows-server-based system. Also, this would allow me to store all profile-related stuff in the same place for Windows as for Mac and Linux -- on our home account RAID -- as I'd wanted to do in the first place. And, in general, it should be much easier -- or at least not too difficult -- to maintain.
A last note on the timing of this project: I just spoke with my boss about the fact that I'm way ahead of schedule and have been thinking about implementing our unified password server over the Winter break. Lately I've had some misgivings about doing this, and he echoed those sentiments. His take was basically, "If it ain't broke, don't fix it." Always sage advice. And as gung-ho as I am to see this working, giving it some time and implementing it over the Summer will give me more time to plan this more carefully and test it more thoroughly, so that we can iron out problems at the beginning of the school year -- when students' work is not quite so in-progress -- rather than at the end -- when students are trying to finish their theses. This seems like a wise approach, and at this point I'm leaning toward erring on the side of caution.
Finally, credit where due: In-depth information on NTFS quotas can be found on this Microsoft page, which is where I lifted the images in this post 'cause I'm too lazy to figure out how to get good screen captures in Windows, and 'cause those images described perfectly what I wanted to show. I believe the images are in the public domain and, therefore, legally usable in my post, but if I'm wrong, I apologize, and if I need to take them down, someone can let me know in the comments section.