You're about right about lactic acid - although LA levels drop within an hour after exercise, not during it. But I don't think it's just lactic acid we're talking about, when discussing the concept of a recovery ride.

The point of recovery ride, as I've understood it, is to open up your muscle circulation and help to get nutrients in and metabolic by-products out. For example, when doing weight training, your muscle metabolism is boosted for up to 24 hours, busy building up stuff and repairing all that micro-trauma that your muscles take during the exercise - it's the repair process that adds a touch of extra mass into your muscles after every weight training day. The delayed muscle soreness (DOMS) is related to this repair process, in my opinion.

Also, I think it can be considered as mild massage for opening up the tightness in muscle bundles, that can partially cause the soreness you feel. Also, the recovery ride makes a good warm-up before doing some stretching to further loosen up those tight muscles.

PS. You guys, if you're so sure about your stuff, maybe you could do with a bit less of yelling 'troll' and a tad more of dishing out the facts