And yes, there is an app store on the phone itself (called the Android Market) where you can download apps and games directly onto your phone. No need for a computer. Although a WiFi connection would be handy when to get faster download speeds :)
JellyWeb: Has anyone managed to find the Nexus One photo gallery app and put it on their Desire? It looks way better than the desire one. I only just got mine today, so a bit of a noob... can you do this without flashing the ROM?
I couldn't find any useful info but did only do a quick google... (getting tired!)
NZtechfreak: It revolves around your Google account, of which your email is a part, yes.
I believe there is no problem with adding several IMAP/POP accounts.
Gmail itself is handled differently, its automatically set to 24/7 push by default, but you don't have to use it that way if you'don't want to. For example I have my Google account set up on the phone, and my Calender syncs through that (so that CallTrack works, it automatically backs up my call logs to my calender), but contacts/email go through Exchange sync (since HTCs exchange email software is better than the inbuilt Gmail app IMO, one of which is being able to set my Push hours).
NZtechfreak: I'd try taking out the card and reinserting it, that happened once to my card - somehow it became "Unmounted" (a setting from Settings -->SD card before removing the SD card). Reinserted and restarted and all has been well since.
Probably worth also copying over the original cards files, including hidden and system files, just to be on the safe side (although I would think the phone should add them all to new cards automatically anyways).
Yup, I've got it on my Desire. And no, you don't need to do any flashing. Although it doesn't integrate with the Desire fully though (ie: clicking the "open camera" button in the app crashes the app).
Although it looks flashier than the Desire gallery app, personally, I prefer the native Desire one, because the N1 gallery app takes forever to load your photos. It's good if you're showing off a few photos to friends, but I wouldn't use it for daily use.
kiwitrc: Is the storage card icon you mention one of the ones listed here, near the bottom of the 2nd list? http://nimbu.amorvi.com/2010/04/htc-desire-new-user-guide/