I would create a web server farm with lvs (www.linuxvirtualserver.org) under linux (logically). This should be a HA load balanced enviroment for shared hosting services. The main problem is about storage. Supposing that it grows, how can I "add" disk space to the entire cluster? Is there any filesystem that support that feature? I know PVFS (Parallel virtual File system), but it hasn't got fault tolerance, and CODA uses server-client infrastructure, and I want a decentralized filesystem.
Finally, I have the same problem for database load balancing, replication and extension (in case it gets small).
