>hamlet is by far Yesod's best feature
In your opinion.
>but once they actually start using Hamlet, they love it ... not a single user has wanted to switch to an alternative.
Hamlet is one of the major reasons we're using snap instead of yesod. Of the 5 devs here who worked on a test app in yesod, the most favourable reaction to hamlet was "well, I guess I could live with it if I had to". Just because we didn't come ask "how hard is it to use a decent template system with yesod" doesn't mean we love hamlet. We just tried out snap and happstack instead, where using whatever template engine you want is obvious and trivial.