5 things you should know about developing for Google appengine

I've been building a few apps on google app engine over the last year (after spending 10 years doing java apps), and here are some things I noticed not many people are discussing when they mention appengine:

1. It's pay for what you use, but it will probably be completely free for you. The free usage quotas are _generous_ and even when you reach them, the sophisticated billing google has set up allows you to 'budget' for particular resources. Even with a 'budget', _you only pay for what you use_ (rather than the typical monthly fixed fees in play with every other hosting provider).
2. The google appengine team is working at a blazingly fast pace. In the last year, I've seen a flurry of releases with some of the most requested features and improvements (cursors to work past the 1000 results limit, auto-datastore retries, secure connections by default, better instrumentation/optimization tools, etc).
3. Use Python unless you can't. The learning curve for the language is small and your web apps will be slimmer and more lightweight (as opposed to going the java route on app engine). There is a reason google hired Guido van Rossum and there is a reason he is working with the app engine teams. Python feels closer to the metal and anytime you're working with something that's constantly evolving, it is beneficial and efficient to be able to get to the things you need to without being roadblocked by too many layers of abstraction.
4. Your apps deploy to appname.appspot.com by default. This is interesting for a few reasons: 1. It's free, 2. There are a limited number of names available, and 3. It means that to look like every other web app you'll most likely end up purchasing and linking a separate domain to your app. You can easily set up a custom domain+cname (i.e. - www.myapp.com) to use your app, but not yet a naked domain (myapp.com). Most apps are working around this by just setting up forwards/redirects with their domain hosting provider.
5. I think this is going somewhere you may not have thought. Looking at the resources Google is putting behind app engine, and the way it lowers the cost of entry and the cost of infrastructure management for custom applications, I can tell you one thing: A behemoth like Google, that has already infiltrated enterprises with a 'drop-in' search appliance (after honing the inner workings with consumers), is not a far jump away from creating a 'drop-in' app hosting appliance/grid (after honing the inner workings with its consumers -- app developers).

btw, this post is a really elaborate excuse to test an app-engine based webapp I hacked together for myself to tweet out my new blog entries (example) automatically.