you have to check each one individually silly! :)

Keep in mind... I would only mass portal load like this if they were all similar with limited module sets (the same modules used in all the portals).

Seriously... if you were upgrading 200 DNN installs you would check all those individually too.. the big difference is time.  with the separate installs you have a more gradual timeframe of backup/roll/check/backup/roll/check etc.  with all of them on the same portal you have to check all 200 quickly :)

For minor releases we don't actually check every portal.  We check the functionality of each installed module by picking on a couple of portals that use those modules.  It's a lot easier to check 20 modules, than 200 portals and in those cases all 200 portals are very similar.

For major releases (like going from v5 to v6) *every* portal *AND* *every* module has to be checked - we backup the host and put the backup on a test server... upgrade the test server, find/fix what broke and then repeat on the production site.