Interesting question! For me, I think I glomp onto characters to love, so if the writers mess around with the characters, making them do OOC things, or writing plots that don't make sense, I tend to loose interest. Grey's and BSG fall into that category for me, but even then, I'll watch for awhile after I've lost interest, hoping it'll pick up again. I'm more likely to just forget about watching something, rather than make a conscious decision not to watch...if that makes sense?

For SGA, even with all of the changes, I'm still enjoying the characters who are there, so I'll keep watching! And some of the spoilers have renewed my interest. :)