One of my current intentions is to play with server clustering once the Raspberry Pi is in volume production and the 1-per-person restrictions are lifted. I have a long-term background in parallelism and concurrency --- my doctoral research was in the topic, and I lectured on it later as well, so it's quite dear to my heart. The very low price of the board makes this feasible with a monetary outlay far below anything else, so I'm really looking forward to an Rpi clustering project.
I'm sure that I'm not the only one thinking about Rpi+clustering. 
If anyone here has this kind of application in mind, or just general interest in the subject, please keep in touch and post any interesting links you may find on the topic. Once there are millions of the boards around, this could be a very popular area. 
Morgaine.
