My driver's seat has been squeaky since the day I got my Prius (factory installed leather). I too will have to check out that clip. I just figured I'd have to take it to the dealership, and I've been too lazy to do it thus far.
I've had the same problem with passenger seat squeakiness. I bought my Prius last summer, so I wasn't sure if it was the cold, or just time and use loosening up some plastic parts. Looks like there might be a real solution developing though. I'll try looking for that plastic clip and report my findings as well.
If I push on the seat front, top or side the squeak stops until I let go. I can't seem to locate the exact spot it is originating from.
So, I looked around under there, and I saw some yellow clips, but that didn't seem to be my issue. This image shows where my squeak is coming from. That's the right-rear of the seat, and it's where the plastic skirt on the back of the seat overlaps another piece of plastic. I lifted up the overlapping piece a little and the point of contact shows enough wear to convince me that's the source of my squeak. I haven't patched it yet, but I'm guessing a piece of tape or something either softer or with less friction will do the trick though.
I finally found a way to take the side plastic panel off the seat without breaking that one clip! Unfortunately I broke the clip before finding the solution. The cover that the clip is attached to has a screw on the lower seat side. Remove that screw and you can take both covers off together without having to break the clip. I put some black electrical tape on the inside cover. It was clear there was rubbing going on in there and causing my seat noise.
My '07 fabric seat does not squeak even when its cold. Maybe all you squeakers weigh too much, I only weigh 230 lbs
Having fabric seats has nothing to do with the squeak. It has to do with the seat side trim rubbing on the seat hinge. I took pics of the removal. http://www.flickr.com/photos/21580284@N03/
