I've done 4 batches - 1 liquid, 2 with re-hydrating, and 1 pitched dry on top. The only one to have fermentation problems (due to stalling, perhaps due to colder storage temps) was the one I pitched dry. It went like heck for two days, then apparently stopped in its tracks.
When you consider the fact that re-hydrating takes only about 15 minutes, and you can do that when the wort temp is near pitching temp, and it takes only a minute of effort or so to re-hydrate, it's really a no-brainer for me. I will always re-hydrate from now on. Compared to the amount of time everything else takes, this part is gravy, and why risk the quality of a batch that you've worked so hard on?