Well, it's finally out (managed to look at the blog at one minute to midnight and reckon I was pretty much the first to download the app. i was getting 200k/sec, not the terrible 3k/sec some people were getting, so I'm well happy about that.

Now, I run an Exchange environment at home as part of a learning curve for my job. I've run Windows Mobile phones and friend tested a Nokia N95 with an Exchange client on it, all with great success.

The iPhone is far far better than any other client I've used for Exchange ActiveSync (AES). Push works extremely well and calendar and contacts update particularly quickly, (ie. instantly).

Listening for the beep of new mail in my Outlook client (Office 2003) connected locally to my domain, the iPhone takes about another second to beep suggesting new mail. VERY impressed. Windows Mobile clients were a lot more sluggish and sometimes notification wasn't even present.

Downsides are as follows:

NO Notes (I use these a lot on my work BlackBerry with our BES)
NO Tasks (also use these a lot at work)

So far, other than that, it's faultless.

Contacts/Address Book is painfully laggy, which I'm hoping will be fixed by Apple soon enough.

If you need to connect to an Exchange environment remotely, then AES is fantastic in the iPhone/iPod-Touch.

I'm not saying this from an Apple fan-boy point of view either. I work purely in Windows at work (and enjoy it) and bought a MacBook purely as a second machine (other computers are obviously Windows Server 2003 and Windows XP) to look at the web in bed etc and enjoy using both types of machine.

Have fun people, it's been worth the wait!

Cheers,