Great thread ! I feel much the same way as you Dave (TF). I'm a very comfortable and confident rhythm player, all the way up and down the neck, but always feel my soloing is stifled, uncreative and generally rather cr@p. I don't think it's really down to a lack of technique. I just don't seem to be able to think of good stuff to play.
In a way that is strange because I used to play sax for years, and was a really quite accomplished improvisational soloist on that instrument. I just can't seem to translate what I use to do on the sax, back to the guitar.
I think some of it is definately what Dave_mc was on about earlier in the thread about different ways to make one not interesting with bends and vibrato. I really don't feel I make the most of that at all.
A lot of it also just comes down to effort. I get rather bored at widdling, soloing, playing scales, etc, anything like that, so I don't practice it much.
This thread has inspired me to put a bit more effort in though !