I use ExchangeMyMail and love them. Like others have said, I think it just depends on your needs. In my business, I'm on the road alot and make changes to my appointments as the day goes on. I use those times for billing purposes when I get back to my office at the end of the day. It's just nice that their all updated between my BB and Outlook without having to sync. As for email, it's awesome to get push email. I constantly get compliments on how fast I return emails in the field.
Just my two cents