Starting tomorrow, we're upgrading our servers to match the growth of Wikidot. We plan to make the upgrade on-line, without any noticeable service outage, keeping 100% uptime. However, if we encounter problems, Wikidot (or parts of the service) might go off-line for a while, but we will try to make it as smooth as possible — and we know how to do this.
Currently your data is kept not only on different servers in the same datacenter, but also exported (also through live database replication) to remote datacenter (EC2). In case something goes wrong, there are several ways to reshape or restore the service, even at a completely new location.
Anyway, our internal infrastructure is quite an interesting topic, and I hope Pieter will give me a chance to blog about it a bit more. The good thing (which I am proud of) is that it is scaling nicely and we still have plenty of room for new users, new sites and interesting projects!
Update: the upgrade finished smoothly.