BIS will poll your email account ever few minutes or so. I can't use it as it does not play very well with MS Exchange 2007. Redirector essential forwards your emails to the BB. You won't have to leave your computer on if you use BIS.
Neither allows wireless sync of appointments, contacts, etc. I think that is changing on newer releases of BIS.
This is my first BB and it didn't take long to get used to the sure-type. I think it is pretty good and rarely do I have a typo. I use it for short messages and replys.