About my current skill level: I do use regex occasionally, but its enough of a bugbear to me that I’ll avoid it unless the alternative is very inefficient or infeasible. Usually I crib other people’s expressions and modify them until I can get them to work. What I’m looking for is to get to a level where I’m really comfortable with creating them on my own. I’m pretty sure I could handle something intermediate level.
(Filed here since regex appears in several programming languages, though each language’s implementation varies slightly)
I usually just use whatever is available as an online resource. @rpkamp mentioned regular-expressions.info, which is a great resource, but where I work, it’s blocked. So, wherever Google points me that isn’t blocked, that’s what I use.