Well the BB excels at ease of use for messaging and sync with Outlook.....as I said it before, BB excels at syncing everything including categories and contact pics.
S60 is great because it offers the best of multimedia and business together. However, if the BB comes out with a great camera and music player. I think I will be back to a BB. Sorry, but one press to get to everything like creating a message, contact search in phone mode, having IM run in the background without draining huge amounts of battery, and I love the phone being able to dial extensions by itself, and a host of other easy features make the blackberry a good device. Not the prettiest OS, but good for use.
However right now it's still the E90 for me until that happens....that's why I was hoping so much for the E71i to be announced. I'm sure it will be the E90 in a lighter form factor.