[Martin-Barbour]

Exchange support works really well, all contacts, calendar, emails and folders sync up without any sort of complicated madness.

There is a bug with exchange support and OS3.0 where the iPhone appears to forget about the exchange account for a few minutes before it all reappears again, something to do with the way it handles certificates, but it's been reported on a number of forums so will hopefully be fixed in the next release.
I've had a 3GS for about 1 month now and have only seen this bug once.

I've currently got 4 email accounts setup on mine, exchange, 2x POP and IMAP, all work well.

The keyboard software has some cool predictive text tricks which monitor your keystrokes and movements between strokes, so even if you don't actually hit the right keys more often than not it will write the correct word. This actually works really well...

Leaving all of your Push and data connections switched on can be very expensive when overseas, it's worthwhile switching that off before you take off unless you've got one of the discount data bundles.

Hope some of this helps....