Just read a great post/article from The Logo Factory, a professional design firm that specializes in--you guessed it--logo design. The post talks (complains) about several factors that lead to logo theft, like contests, lazy people, etc. Ripping off someones trademark is low but illegal. The worst is when people rip off ideas that aren't even that hard to think up in the first place.
Granted-- design work is difficult. I spent a few hours tweaking my latest K! idea, which is by no means the best logo in the world, but I like it, and that's what counts. It hit me today though, when I stumbled onto a site called Add-Art, that gives you a plugin for Firefox which--similar to ad blocker plus-- changes all the ads on a page, in this case to art. Neat idea. My issue was that I immediately recognized the logo as that of Sherwin Williams, a well know paint brand in North America.
If you're trying to establish yourself or your company as legit-- ripping off a logo is a no no. Inspiration is one thing, but being a 'copy cat' as the Logo Factory dudes tell us-- is another.