I think it's not necessarily good or bad, you just have to know the impression that you're creating. Back in 2000, L33T would've been cool or funny. In 2004 it might've been silly, a joke name. Now it will feel like a lame or outdated name... but that's okay if that's the impression you want to create.
I have a story I'm working on where all the characters go by their screennames, and so one of the characters is a hacker who goes by H4CKM4ST3R. At one point in time that could've worked without irony, but at this point it's an eye-rollingly dumb name -- which means the character comes across as kind of immature, and out-of-touch enough to think old memes are still cool, or someone who thinks ironically dumb names are funny. Since that's what I'm going for, the name works; if I had wanted him to be cool and intimidating, it would be distractingly bad.
So I think it depends on how you want the character to come across!
