I didn't expect lower() to have much of a speed impact and the query plan shows that the difference between doing a straight '=' or '~~*' and lower() is only 44msec versus 54msec.

My indexes are pretty tight and it's a well (and often) maintained database. With millions of records, it has to be. :)

The reason I didn't use LIKE is that I'm trying to allow users to create usernames that contain any characters they want without having to manually escape dozens of special characters myself.