I got a curve yesterday on Orange and I love it, the screen is the clearest of any phone I have owned, the phone takes a little while to get used to the menus etc but once you are it is immense.
The wi-fi net access is really quick as is the GPRS net access, it costs an extra £5 a month on top of your line rental for access to "The Orange Blackberry Network" via GPRS as they call it, but for this you can surf the net and download emails 24/7 at no extra cost, the wi-fi net access doesn't cost anything and the phone searches for wi-fi networks as a priority over GPRS networks.
The guy in the shop said that if you want it for business use and are using the net all day get the Bold as the phone is slightly bigger and the keys on the keypad are larger, but I went with the Curve as it has a 3.2MP camera as opposed to the Bold's 2MP camera and it is slightly smaller so it is less of a brick to carry around.
Andy