As people have mentioned, the 770 is pretty much in it's own class. One of the downfalls of it's acceptance is that it does a little bit of everything but perhaps not as well as dedicated devices.

I apologize for not having time to dig for links as I'm at work but check out Deja PIM. It's free, though if you want to use their services for synching there's a nominal monthly fee. I've used it on and off and it suited my needs just fine and didn't seem buggy at all.

So far as a graphing calculator, I seem to recall a project where someone emulated a Texas Instruments graphing calculator (complete with scanned graphic of the hardware) and slapped it on the 770. Check www.maemo.org and root around the apps section (most likely in the Work In Progress section).

I've said, and will still say, if you want a full fledged Office Suit, get a laptop. Gnumeric has worked great for me but it still hasn't been completely converted to the 770's interface so some menus are a bit scrunched and illegible. I haven't tried AbiWord but I can't imagine using the 770 to hammer out a document several pages long... even with a bluetooth keyboard I personally wouldn't mind formatting it later. That's me tho.

Otherwise, from my experiences, I love this little thing! There are more and more apps being ported/written every week that keep giving it a new lease on life. There's a new edition of the OS due out this month and I think a lot of devs are holding back until that comes out (there are changes which make current apps incompatible with it. This can be fixed of course but that's an issue of free time to do it)

I'd recommend hopping down to a CompUSA if you're in the U.S. and trying one hands on. I drove to Michigan from Toronto to get one and don't regret the trip for a second. And I hate Michigan.