I am an avid fan of the VFF's. I purchased the Classic's last year around the middle of April right from the Vibram website. I also purchased 3 pairs of Injinjis from the REI website. I had done some reading prior and thought I would give the barefoot / almost barefoot running a try. (I was starting to get pains in the hips and knees.) I knew the first week would be tough, I cut back on the mileage from ~ 40 to around 15-20 in a week. My calves were very sore by the end of the first week. I knew to expect this though. After that the soreness started going away as my calves adjusted to running differently. I land with the balls/mid foot and let the heel compress down to the ground and then lift up again. The heel does not make hard contact though, just a light grazing. I also make the attempt to keep the toes up. The zen concept of the landing is to think that you should be pulling up your foot as it is landing. You will push off from the ground and this is where the seperated toes really comes in handy. (I try to focus on the flexion as I push off with the toes). It took me about 5 weeks of running in the VFF's to get back to a speed that I was comfortable with and was comparable to prior to using them. I ran in them almost every day except when I took a real barefoot day. (I even did some barefoot completely on concrete/blacktop, can anyone say ouchie.) The VFF's were not meant to do that much roadwork. They will wear out quicker. Within another month I was running just as quick in the VFF's as I was in sneakers beforehand. But now my calves and feet were stronger. I did start doing something unwise, I tried to change my foot landing to try and compensate for an old ankle/foot injury. I wound up getting a stress fracture and was out of running for 5 weeks. (Do not drastically try to change your natural pronation/supination.)
Luckily I had swimming to keep me going (you can swim with the legs isolated). I was back to running the day the doctor said all better. I now wear an ace compression bandage during every run (just in case I slightly twist the ankle, it helps to stabilize the ankle).
I have since the fracture changed to running hard runs with sneakers on pavement and easy runs with VFF's on grass/trails. I did not use the VFF's during December-February due to cold. I am enjoying using them as everyday walking footwear and easy run footwear. I did adopt my sneaker running to landing the same way ( or as close as possible ) as when using VFF's. I have noticed that I do not get the calf soreness anymore. I even did a 7 mile run with them on and did not notice any soreness. I will caution that stones will hurt, the rubber sole only protects so much.
In regards to arch support, for running and walking the arch support comes from the arch of the foot itself where it should be coming from. (I actually had someone ask me this when wearing them, the person said "What supports your arch?", my answer was simple, the Arch.) I have not disavowed sneakers, as I do use them, but I think the foot has become lazy with modern footwear and getting back to a more natural footwear would be beneficial for most people.
My fastest 5K time with the VFF's to date is 20:08, that was in mid July of 2008. If or when I do another 5K with the VFF's on I will post the time.
Fastest 5K time from last year was 19:50 with sneakers (fastest I could run after that was 20:08 with sneakers).
Current fastest 5K time is 19:11. (Expect to be around 18:40 this weekend.)
I really put on some speed after the stress fracture. I am shooting for 17:30 - 17:45 by October of this year.