We were not experiencing any particular issues. We liked the look of Messenger and it has hooks into Backbone such as hiding notifications on navigation (which we ultimately ended up disabling as some chorus toasts are triggered as you are navigated to an error page, so it was hiding too fast. Though we kept messenger regardless.)
It's a pretty painless migration - not sure what kind of issues you're having with jGrowl, but for the effort required I'd say it's worth seeing if the switch solves it.
From a quick 'git log grep=toast' here are the relevant changes.
dc09881b51c8be265a12707454b425ae145a78dc (Initial Messenger commit)
7fd0326f67508acd45c2264c40142af2f6a96404 (reset z-index)
9302fba9aedfffc4bba7bca222f7bc51c82c162d (disable hide on navigate)
7d941f2ca490c10aed341466fad64735c0bff848 (stub in spec_helper so toasts don't fire in jasmine)
- Robbie