rish3 - 12:44 am on Mar 14, 2013 (gmt 0)
They may be spammy and annoying, but Google currently values them pretty highly. Can I prove that? No...too many variables, but I can find you plenty of sites ranking #1 for competitive terms that have a LOT of guest post backlinks.
I suppose it's possible they are ranking despite the guest posts, but in many cases, the guest posts appear to be strongest backlinks they have (in terms of PA/DA/PR/etc).