Yes, I do try to tailor the cv and application letter to every job I apply for, calling up their contact to have a bit of chat, and to show that I'm really interested. I haven't asked for why I haven't been picked for interviews.
I'm a bit unsure weather that's a good or bad idea. I have a feeling that they might find that a bit whiny, and might reduce my chances with that employer, if they are seeking more people later on?
I don't know, maybe I'm just being ridiculous.
Also, I think most of the time you'll probably only get a generic answer like 'overall assessment' and that sort, so really not providing any answers.