I tried last night (after turning of all websites, applications and even SQL jobs that use the DB) to update a bit column to 0 on a table that contains 227 million rows. After 5.5 hours and it being 5:30 AM, I had to give up and rollback the change (which probably took about 3 hours).
Strangely, a week prior I update a DateTime field to '1/1/1900' in the same table without any issue. I don't understand why I'm not able to run the update in a reasonable amount of time. Perhaps I need to delete all the indexes first and then build them back up after? That's a royal pain.