I also transited the tunnel a week ago on my way back to France. I was pulled for a security check and swabbed, my number plate was also checked. Whole process took about 2 minutes. Checkin took about 90 seconds after I'd joined the one car queue. Passport control 20 seconds with no queue. The reason the tunnel can process it's passengers so quickly is because it has sufficient infrastructure to do so. The BAA London airports do not.
CC, the reason a seaport (or a railport) is relevant is because it offers a viable alternative. I thought about taking the plane for this trip but couldn't be bothered with the hassle of LHR or LGW. As a direct result of BAA mismanagement (of it's airports) my money went to Eurotunnel instead of Air France to LGW. I hope Air France realise how often this is happening.