Windows Phone's main problem in my opinion is the lack of popular apps.  Since I have multiple platforms, this doesn't affect me as much but I may switch from Windows phone on my next purchase. 

In the beginning I thought I was really going to dig it because I could program .Net on it, but in the end it became more of a hassle since I didn't want to pay to re-up my Windows Marketplace subscription (and my device just re-locked itself and removed my side-loaded personal apps I'd written that I cannot now redeploy to it). 

I have a few more months before my contract is up so who knows yet.