We've tried PGO with the Evolution engine every major Visual Studio release for as long as I can remember and each time we fail to measure a significant performance increase -- certainly not anything worth the substantial time and effort required to do it regularly.

Our most recent test of LTCG was actually interesting because it seemed to move the needle enough to measure (but not enough to suffer). It appeared as though it optimized the vast majority of the code for size (inlining sparingly) and we speculate that the improvements to cache usage were the reason we saw improvements.