As everyone knows, this has been done before and we've (including actual lawyers involved) already years ago concluded that this company has no copyright on the gameplay or concept or anything. What they have is trademark(s) so staying out of actually using their name(s) is probably a clever idea.
Old data from 2006 when Tetris LLC sent mail to the Rockbox project: http://lwn.net/Articles/200179/
As others have mentioned: a common practice that seems to be going on when some of these law firms contact you and are going out on a limb, is that they attach a contract which they want you to sign and agree to things, as if you actually go ahead and do that and you wouldn't stick to that agreement, you're suddenly violating contract law.
If I want your opinion, I'll ask you to fill out the necessary form.