ITTs are NOT great for ebooks. Ebook readers are great for ebooks. ITT's are "meh" for ebooks.

On another note, PDAs are dead. Most folks nowadays use either smart phones or these UMPC type devices. In fact, I ain't even heard the word PDA till I read this here thread.

I've read a few books and *lots* of scientific journal articles on my N800, I like it a lot as an ebook reader, YMMV.

I use my ITT as a PDA, it's not perfect (pretty close, good enough, bye bye Axim) but I really have no need for a cell phone and have *zero* interest in signing a contract or paying anyone a monthly fee for the use of a PDA... again YMMV

I have a Palm Tx (never use, collects dust), a Palm Centro, and an N800 that I love. Without a doubt I can say the Palm PIM apps are 100% better than anything on the N800, and if you're planning to switch over, I would bet money that you will be disappointed. Not to say that cant change, GPE looks like it has promise, but Palm has been at it a long time, and has it perfected.

I didn't think much about PDAs either (although I could other people were using them) until I finally got myself a Palm. Very quickly I couldn't live without it, it's like getting an extra little brain to keep track of all things I didn't know needed tracking.

I still carry my Palm PDA in addition to the N800, because as Scrabbler said the Palm is just so much better at those things. (GVM can make up for some, but not all, and nothing that really needs alarms.)

Smartphones are not for me, even if they had good PIM (which they IMO mostly don't have) - their screens are too small for me (and getting more of a problem for every year..), unless the phone is as big as a PDA and that's a bad phone as far as I'm concerned. So, for some of us, PDAs are not dead at all and won't be for the foreseeable future.

I bought my N800 specifically as an upgrade from my trusty TX, and I can honestly say the TX hasn't been switched on since. I've got the Garnet VM installed, and have played around with it a little; one thing to note is that when running fullscreen, scaling is a bit ugly - 320x480 doesn't go nicely into 800x480, while at 1:1 resolution, there's a lot of empty space around the palm screen. The one major app that I would have used but wouldn't run for me is Pimlico's Datebk6. Another point to consider if you're a long-term Palm user is that the handwriting recognition doesn't match Graffiti. Although you can customize it, I've tended to stick with the onscreen keyboard.
I'll confirm what everyone else says about the limitations of the PIM software for Maemo; that said, it's good enough for me. I'm using GPE for contacts, and Maemopad+ for memos. I can offer scripts for converting from Palm dbs via pilotlink if needed. The main advantages come through the larger screen - as a result of this, Claws on Maemo beats any of the Palm mail clients hands down, indeed any handheld mail client I've used, and both Opera and MicroB really show up the failings of Blazer, Opera Mini or (shudder) Pocket IE for browsing.
The other major difference is that I stopped using my handheld as an add-on for my desktop, and now use it as a standalone computer in its own right. For example, I no longer sync with my desktop automatically every morning; the N800 downloads and converts my plucker feeds itself. Ditto for accessing files across the network; I no longer need to copy data across in advance, as I simply access my home PC directly over sshfs or openvpn from where-ever I may be. I find the N800 to be a vastly superior machine to my old TX almost every other respect, and the PDA functions, although somewhat limited, are good enough.
Finally, nobody else seems to have answered this - I've just checked, and I couldn't see any way to access either of the card slots from within GarnetVM. There's a way to do so in POSE (the old palm emulator) which is available for Maemo, although I haven't tested it.

NB. Apologies - didn't check the date of the original question; however, my comments may be useful, so I'll leave 'em here.

Your're correct about the limitations in GVM: The current version can't access the cards (except through the 'install' function in the launcher, which can copy .prc and .pdb files to the GVM itself). It also can't access BlueTooth directly (only indirectly, if you use BT as networking in the N8x0. GVM sees the network).

Those limits should be pointed out to anyone who's interested in GVM as a Palm replacement. If you favourite Palm apps need to read or write to SD, or use BT directly, GVM won't do.

Networking apps, on the other hand, work fine. So does almost everything else in fact, except non-m68k applications (there aren't that many). And AvantGo doesn't work (only the AGConnect part).