Thanks for all the great input -- I think I've finally settled on an iMac, as my iBook should be able to struggle on for a while longer and there is a good chance I can sweet-talk my employer into subsidizing a new laptop for me at some point next year.

One more quick question - AppleCare, yea or nay? I didn't get it last time and have had only one semi-expensive repair issue in the meantime (power supply problems, surprise!) -- but then AppleCare would still be going and would take me through to the end of next fall if I had gotten it. It's $200, though. Worth it?