I would love an email option in WHS. So much so, that it would be one of the most important features why I would buy a WHS system. I totally agree with jpennin1 comments. I also agree with johncz points 1, 2, 3 & 4.
The most important features I would look for in a WHS in order of priority are:
1) Reliable storage (either RAID 5 or similar). If a hard drive fails, I don't want to loose any data what so ever.
2) PC backup.
3) Sharing video and photos (and other files) in the home and access from the Internet.
4) Email with access/sync from my Windows-based mobile phone.