In reply to Neil Henson:
I've never seen rats around my feeder either, despite the blue tits getting plenty of it on the ground (enough to sustain a daily visit from the blackbird). I have seen an absolutely huge rat at a feeder on an RSPB reserve though, huge it was!
Maybe the choice of food has something to do with it? Mine are the RSPB coconuts, which are great, just string them up in a tree, the birds love them, and at the end just stick the coconut shell in the garden waste bin.
Hygienic for the birds too, as it being replaced so often should help prevent the spread of infections.