A few years back, I registered a domain name - greenlock.com - for a business idea that I had. It turned out that the business never got off the ground because I was relying on angel investors that were crooks and I was so disheartened by the experience that I've never tried to start it up again with new sources of money.
I used to use a free DNS service - zoneedit.com - to direct the name to my own machine on the internet. It worked out just fine until someone figured out that I didn't have an MX record published and began to spoof my domain and spam people like crazy. When I did decide to start receiving email there, I got hundreds of angry letters from people telling me to stop spamming them. I didn't want to deal with the problem then, so I just shut it down.
I recently had an idea to start using the domain name again. I still own it, but it's been dormant for a few years. So, I've reactivated it and it's just got a holding page attached right now, but I started looking around to see who else might be using the name Greenlock or GreenLock to see if I'd run into more problems with the name.
No fewer than 25 distinct entities that I find are now using this name for everything from public storage companies, to software DRM (which could be a problem for you.. I trademarked the name for this purpose when I incorporated), to plastic containers, Christian rockers, bloggers, file-sharers (I might also someday object to you..), to other off-the-wall stuff.
Three years ago, I couldn't find one, hence the ease at which I registered greenlock.com, greenlock.net, greenlock.biz, but I left greenlock.org alone.. So, someone else has that one now.
I wish I'd moved on technosavant.com earlier. Technosavant.net is more appropriate for what I started this for, but people confuse it all the time..