Best of luck. Especially when you're going to upgrade 2 or 3,000 sites to the next major release.<p>Another big stumbling block I've noticed when hosting large numbers of drupal sites is that drupal uses a very large number of database tables (&#62;50, sometimes &#62;100) to accomplish relatively simple stuff causing big problems on the database servers.<p>If you host only a single site 100 tables is no big deal but when you have large numbers of small sites this becomes a real bottleneck.<p>I believe recent versions of drupal are a bit better behaved in this respect.