Okay, so to be honest, it's 5 AM and I've realized that I don't have much to write about today. So, here are two ideas that have been knocking around in my head lately.
Heated clothing: It should not be too terribly difficult, from any perspective, to run some wires through a jacket so that when a battery is plugged in, the jacket heats up. (For some reason, this idea comes back to me every winter, and then I forget it again come spring. >_>) Obviously, you need to be careful with this or you're going to catch fire and burn to death. For bonus points, there could also be a digital thermometer in there somewhere, so that you could target a geven temperature.
Archive-only filesystems: This is basically a relaxation of traditional filesystem semantics. Traditional semantics are problematic for distributed filesystems, because there's no good way to resolve conflicting updates. However, archives are a pretty common use case, where files are never updated, and never (or rarely) deleted. Therefore, if we relaxed the filesystem semantics to disallow writes to complete files (obviously, you still need to be able to write to incomplete files, and the FS would have to track that bit of state), and to allow delayed deletes (so that the file is still allowed to be readable for an arbitrary amount of time after it is deleted), it seems like we could build something that performs a lot better than the current batch of distributed filesystems, while still being pretty useful.