Hosted vs. In House Exchange

I'm beginning to realize that there might be some advantages to having an Exchange server hosted by a provider instead of building and maintaining one in house. This is especially true for smaller offices, say five to ten users, who could benefit from Exchange's many features.

Many of my clients have held back from going to exchange because of the high cost whether it be for the server hardware and software costs, the extra management required, or the need of a high quality (not cheap) SPAM solution. Many could benefit from the Windows Mobile and BlackBerry integration that Exchange offers as well.

To that end we have interviewed many Hosted Exchange providers and have found one that does excellent work on all fronts, SPAM and Virus prevention, backup and recovery, and ease of management.

What do you think about Hosted Exchange providers? Yay or Nay? Share your experiences.