Hi Dan,
Here are a couple of sites to check out...
http://community.spiceworks.com/topic/78891 (down the page they mention MSDPM only backups up Windows clients...)
http://www.informationweek.com/news/storage/reviews/showArticle.jhtml?articleID=207600575
http://community.spiceworks.com/education/projects/Backup_Solutions_For_A_Enterprise_Business
DPM looks like it will work great with only Microsoft OSs and applications etc. If you have VMware running for example, and wanted to take full backups of your VMs, DPM wouldn't do that, nor would it support Linux etc.
Hope this helps!