I'd never change from Paypal, purely because everyone uses it, it's very easy to use, and I've never had too many problems with it. The only reason I'd change is if a lot of people started using a different service or if the rates became too large..
Well they sure have a better site than those golddiggers :P I didn't like their slogan at all though:
"Your wallet for the internet..."
Here internet, let's share my wealth!
Yep, you guys took all my suggestions. e-gold and Moneybookers have the added bonus that it's slightly easier to write IPN scripts for them than it is with PayPal, too.