I went through a lot of names before I settled on Chiaroscuro, though I've been using it since 96. It's the name I use at RPGnet, and I think I at Malhavoc's boards. There's obviously another one here, though. Hell, it may be that I registered it and then forgot, thereby preempting my own name.
So far as I know, it's pretty unique. It's my creative way of getting to be "Phoenix" while dodging the ubiquitous character of that particular moniker. As well as firmly cementing my 'military nerd' or 'geek' credentials.
I have never had trouble signing onto a messageboard with it.
Someone snagged "Mercule" on eBay. Otherwise, never had a problem. Which is good, because it's just a random couple of syllables I thought would be good for an elf character name.
Oddly enough, Mercule is apparently a surname, though I've no idea of what origin.
I myself only have trouble on some sites that don't let you use spaces... I also got some Lady chick using my surname... and really I cannot figure out why either... :\