I have to say that I've seen of Snap looked a lot closer to my favourite framework, Flask, than what I've seen of Yesod. The big problem, IMHO, is the lack of a good multi-database persistence story for Haskell. You have several good, mid-level database layers ({mysql,postgres,sqlite}-simple), but they don't even offer a common interface. And HDBC's performance, from what I could read, is not really top notch.

And then you have Persistent, which works in its own monad (I'm not sure if it works as a second level cache, because it's not terribly well documented) and with a good helping of Template Haskell tries to be an ORM. Unfortunately, it's not terribly powerful (numeric IDs only, no complex joins, and it doesn't look like you're expected to write the mapping between your model and the table(s) yourself, so forget about legacy databases).