Yeah that makes sense... I don't play a wide range of games though. Right now I have only one that I play right now (Guild Wars). However, I think 30GB is more than enough for a 10GB OS and a couple or more games that I may play regularly. I just don't have the cash right now to spend $200 on a single harddrive that doesn't hold much, regardless of speed. Even $120 is pushing my budget for a 30GB SSD. I'd mainly use the SSD for the applications I'd use regularly (like Firefox, and Guild Wars for example) and put things like media (music and video) on the HDD, and anything I wouldn't use a lot (such as Open Office).
Even if I got a SSD large enough to fill with games and whatnot, wouldn't I only be benefiting from a quick install and update processes, then launching the game? Not actual runtime of the game? Guild Wars, in particular, doesn't require any saving/downloading unless it's to get updates, which aren't that often (seasonal events excluded; about once a week).
So in the end, I guess it'd be all up to me to determine which applications get used to enough to warrant faster opening of the application(s) and reading/writing of files.