For a long time, I had a mesh body but not a mesh head. I hated the original pre-bento male heads, they were terrible. When I came back to SL last year, I demoed several heads and found one I liked that still felt like "me" (especially after buying a skin for it as well). I think that's one of the reasons people don't make the transition to a mesh head - many people are very particular about their avatars and identify with them, and it can be a long process to find a mesh head that you feel comfortable with.