Not to be a wet blanket... (Yeah, yeah, I know, anytime you say something like that, you're actually being one...hush...

)
So far, petitions do pretty much no good in getting their attention, really. A petition does not ensure them getting money in exchange for doing the effort. After all, one should get paid for one's hard work. All a petition does is show that someone
claims that they'll buy the game if it's ported to Linux. Now, if they have, say five or ten thousand signatures, they might begin to pay attention because it'd be reasonable to them to assume they would see something like 1-2k
purchases from that work at that point in time.
By all means, sign the thing. Just don't expect anything different from the Diablo II, WarCraft, etc. petitions of the past. The only way they will really be convinced is if they see numbers of sales from other publishers and developers that braved the leading edge. Oddlabs is doing us a big favor by releasing their numbers- it's actually helping. I'm hopeful we'll get some adequate sales with Ballistics, Bandits, and Disciples when they come out so that'll be in our favor as well.