I've used our own in-house implementations of some of the .Net RexEx functions on seemingly large datasets (several million records each), mostly to help clean up, validate and parse addresses, city-state-zip (or province), etc.
Beats pure SQL functions like Hulk did to Loki in the movie, especially in understandability. I'll take teasing a complicated Rexex pattern over scads of nested SQL functions trying to do the same thing.
one I really have done lots of is to do is keep expanding on a pattern like this: '(Company|corp|corporation|inc|llp|llc...)'
beats continuing to add "or field like '%new_match%' ..."