I believe that a lot of the evidence on these forums seems to point towards the conclusion that rogaine foam is less effective than the liquid. The shedding that people experience after switching from the liquid to the foam is almost identical to the sheds that would occur from simply stopping using the liquid. Also, any results from the foam seem to take a LOT longer to become apparent than 't they would otherwise do with the liquid, wasn't it also true that the 2% solution took longer to produce results than the 5%? Again, this indicates that it is less effective.
However, saying this, I think that the foam vehicle is actually more effective than the liquid vehicle. If you took a bare piece of skin and applied the same amount of foam and the same amount of liquid to it and let it dry, the foam IMHO would absorb a lot better and produce better results. In my experience the foam IS effective at growing hair on the temples, albeit not fully thick 'same as normal' hair. I think this is because I am able to apply it straight there and rub it right in, and so all of it is getting absorbed into the follicles.
Therefore I think the foam is simply less effective BECAUSE of how we are applying it. Even if I apply it straight to the scalp in areas that are thinner in the mid-scalp, a LOT of it is going to get into the hair and not onto the scalp, while with the liquid you can pretty much ensure you are getting it to the scalp, and so it would be more effective than the foam.
If you have a bald patch then the likelihood is that the foam will be more effective for you because you can rub it straight in and not get it into your hair, same if you want to try and regrow your temples. If you have diffuse thinning of any form then the foam simply won't get enough minox to your follicles.
Anyway, this is my opinion from what I myself have experienced and from what I have read on these forums. Does anyone else agree with this? We have a long thread about the foam results, people are asking to get some kind of consensus about it, well this is what I believe to be the consensus on it. If you can get it to your follicles then you'll get good results, otherwise you're better off with the liquid.