The only time I tried nudging an agent it was someone who imagined herself an immovable object. This was in 2006 and I'm convinced I'd still be waiting for her to reply if I hadn't emailed her and said to forget about it.
Oh, wait! No, there was one other, whom every time I nudged her (at 4 month intervals) she either asked me to resend my stuff or said she was getting to it, orI should send it to her son, etc. A friend of mine (we'd pitched at a conference) had the same experience of this woman. At one point she emailed me and asked me to resend the material, and I never bothered to respond to her.