E-mail worked right out the box - and one of the first things I had to do was setup my account with T-Mobile's Blackberry service. This has to be done using the phone keyboard, so remember your username and password carefully. Luckily my default choice of usernames was available! Once setup you should complete the customisation at the website. I've hooked up my Gmail and sandm.co.uk email accounts.
T-Mobile's provisioning for Blackberries on Web'n'Walk is slightly broken - expect to wait 12 hours or so to get online fully with an activated Web'n'Walk account. Once online you'll need to manually switch the browser from the somewhat broken default T-zones configuration to the much more friendly Web'n'Walk version. This will let you use the Blackberry Help site - so you can download additional themes, games and applications from RIM.
There are versions of Google Maps and Yahoo! Go 2.0 for the Pearl. However they won't work until you manually set the APN in the Blackberry's TCP settings to "general.t-mobile.uk". Again something that isn't provisioned by T-Mobile.
More notes to come.