I've got a pretty hefty 13 or 14 lb maine coon mix; and although he HATES to go in the carrier to the vet, he fits OK. It's one of the soft sided ones with a shoulder strap that would fit under an airline seat. (I frequently take both of my cats to the vet at the same time & needed to be able to sling one of them over my shoulder.)

I agree that I'd take my critters with me on the plane rather than in cargo -- too scary!

My mom took a cat that I rescued with her back on the plane to her home. Used the same soft sided carrier; worked fine. With changing planes and all, it was about 12 or 14 hours, and the cat did great. They did make her take him out of the carrier for security check, so I'd recommend you have a halter and maybe a leash on your cat in case it freaks and tries to run off.

(Are they completely STUPID about cats??? is it going to take somebody suing the airline because their cat was terrified and got loose and ended up dead???) Can't they Xray the carrier to see that there really is a cat in there??