I am loving Heroku for the exact reason described in this post: no sysadmining. At first I thought that wasn't possible and expected all kinds of issues with gems etc, but so far everything I've tried really does Just Work™.

This may warrant a separate question, but I've seen various posts here and there about running Ruby/Rails on GAE using JRuby. Does anyone have any experience as to just how realistic that is as a deployment option? I can imagine it being full of headaches, but I would love to hear from someone who has either tried it or is actually running it on a production app.