In terms of deployment for new apps I am going to go with heroku from the outset. Other key/value datastores such as CouchDB, Cassandra and MongoDB look very interesting, but I have yet to find a use case for these in my current work other than for playing with.

I’m a big fan of Heroku too, it takes all the pain out of deployment — in fact I’d even go as far to say it makes it fun.

I agree that Heroku can look quite expensive, but the free version is really quite impressive — you can handle a lot of traffic before you need to start paying. Heroku themselves say the free dyno should easily handle 10,000 visitors per month — and theoretically 20,000 visitors a day is possible.

http://blog.eliotsykes.com/2009/10/30/heroku-vs-engineyard-cloud-vs-joyent/

Also, you shouldn’t need to install the action_mailer_tls_plugin now Heroku offer an add-on for using Gmail or Google Apps email. (The new add-ons are very cool.)

http://docs.heroku.com/gmail-smtp

Having used both Google App Engine and Heroku, I think Heroku is far, far better. App Engine has promise but the requirement to use Big Table is a real pain in the arse. Django should have Big Table support within the next 6–9 months so that problem may well become moot, but for now Heroku is much more polished and user-friendly.