The name of my next webcomic is used, and the other comic is on SJ in addition to every other comic host out there.
My reaction: Oh well, I'm not changing a thing. I'll just have to come up with a more memorable URL that still makes sense with the title. Or register a domain name (titlecomic.com or whatevs).
I'd never change a comic's name just because there's another comic named that, if the name works really well. Sure, it makes marketing tougher, but if my comic is better, then it'll come out on top. If not, then oh well, not a huge deal to me.