I'm going to go out on a limb and say this show won't ever be taken off the air as a result of ratings. The funny thing is, those who don't support the show are the ones keeping it in the public eye. They bring more attention to it via internet buzz (including threads like this, blogs, etc.), newspaper articles, letters to the editor, et al.
At this point, the only way for it to be taken off the air is if Jon & Kate put a stop to the show .. and even then, can they stop TLC from airing the reruns?
Not that it matters, Kate is continuing to film new episodes:
http://justjared.buzznet.com/2009/05/25/kate-gosselin-rolls-with-ronald-mcdonald/
and we've already discussed the Orange County Chopper filming .. which makes me wonder if Jon is picking and choosing which episodes he wants to be involved with? Orange County Choppers? yes. Kate's Birthday (Charm City Cakes) and the Ronald McDonald House? No. hmmm.....