Mark Ahlness discusses growing pains with David Warlick's Class Blogmeister service. Basically, David's server has gotten swamped, so he was going to split the database to put older posts in a separate archive (or something like that see here and here). He talked to his hosting service and it looks like they're going to set up a separate database server behind his web server. I haven't done this myself, but I don't think it is too hard, and it is the obvious next step in scaling things up. David should be able to pull it off without a significant amount of time and expense.
However, scaling up a web application doesn't get easier and cheaper from here. If Class Blogmeister doubles in use every year, which I'd imagine is quite plausible, this isn't going to be the last architectural rearrangement. It is pretty easy for part-time self-taught programmers like David, or Chris or me to throw up simple, small web apps. One of the things that separates the pros from the amateurs is this process of scaling up. It's not a hobby, and the costs associated with server hosting aren't going to disappear because of Moore's Law. You're looking at electrical costs, real estate, labor, real world stuff.
David needs to have a long term strategy for dealing with these issues. They aren't going to go away, and the service could easily do more than double every year. If many of the classrooms using Blogmeister turn into schools using Blogmeister, he could be looking at x10 growth or more.