Thanks for the reply.
It's not so much the size of the DB or even the $ cost. It's the amount of effort the client would have to go to. Some instances are used by custom applications built by companies that no longer exist. So contractors would have to be brought in to code an update. Other clients take the stance that they are not internet facing (so security is not that big a deal), and everything is working, so why change things.
I'm looking for a reason to go to that effort besides the instance itself being unsupported. If I can say with confidence that the other Microsoft products that support a SQL 2000 instance (Windows server for example) will become increasingly "hostile" to it, then I have a better argument to take to the clients for an upgrade.
Of course, if Microsoft will continue to take SQL 2000 installations into consideration when creating Server patches, then it's not an issue, but it would be nice to be sure