I get a lot of requests from people to look at their squat online - PMs on forums, Facebook, and YouTube come in waves. Usually requests come from email and when I'm bored, I check out threads on forums entitled "Squat Form Check" or "How's My Squat?".
I enjoy watching people squat - not matter how skilled they are. Putting yourself in another's lifting shoes is always a useful exercise for a coach or trainer when done thoughtfully.
Critiquing a squat video is quite different than in real life - sometimes it's easier, sometimes more difficult. Having a pause and replay function makes seeing you perform a heavy single repeatedly a breeze. However, without proper lighting and a decent camera angle, there are just some things that will be very difficult, if not impossible, to see.
For example, the image of the squat below is from an online video. From this camera angle, posture, lean, knee and hip flexion, and bar position and path are readily visible. However, the angle makes it difficult to see lateral movement. Something looked "off" so I watched it again and noticed a very slight "helicoptering" of the bar. The third time I watched it, I noticed the left heel coming off the floor. It's slight, but pretty evident here.
So, here's the deal: if you want worthwhile input on your squat form, don't be stingy with the film! A side view like the one above is good, but having the addition of a set shot from directly behind or in front of the lifter will show lateral movement of the feet, knees, hips, and barbell much more clearly.