Doesn't look like they hold on to the data if you remove a computer from your CrashPlan account: http://support.crashplan.com/doku.php/how_to/remove_a_comput...

(I do like CrashPlan, but this seems to be common practice with data storage services.)

Removing the computers associated with a CrashPlan account and then cancelling the account looks like it'll cause a pretty big headache.