When I find a tab I like I will 5-star and favorite it (and sometimes drop a comment). If I make some changes for myself like transposing it to a capo or such I'll still give it 4 or 5 stars.
I can't really bring myself to give a tab a poor rating My mother always said "If you can't say something nice, don't say anything at all" lol. I'm pretty picky about what kinds of tabs I like to play and I get turned off by the littlest things (which is why I make so many tabs for myself)
Even if the rating system is changed to thumbs-up and thumbs-down, I don't think it'll affect the way I rate tabs.