David:

Are you talking about DRI, or "cascading" actions? Note that DRI is only primary key/foreign key constraints. The cascading stuff is not necessary for enforcing any kind of RI, and is only there to make life easier in some cases. If it's too slow, turn it off and write your own scripts.

If it's not cascading actions you're referring to, I'd be interested in why your deletes are so slow that they require taking the server offline. Sounds like you're missing some key indexes to support those deletes?