My first project - set up a CouchDB cluster fronted by memcached and run a simple PHP application on top of that.
The architecture I'm thinking of looks something like this. I'm sure I'll refine it over time after playing around with it, but starting fairly simple first:
- A web tier running Apache and PHP
- A memcached tier
- A CouchDB cluster tier
I think it's cool that the same qualities you need for peer-to-peer file sharing are valuable for server-side clustering - even distribution, good performance when nodes come and go, and robustness under heavy changes to node configuration.
Once I have something working, I'll let you know my experiences. Then I'm interested in trying this with SimpleDB and Project Voldemort... I also want to take a look at MemcacheDB. So much interesting stuff, so little time :)