I have heard this too. I am just about to do my cambelt so have invested in a replacement water pump from GSF carparts. The replacement pump is made by ruville and has a brass impeller interference fitted onto a stainless steel shaft. My mk4 is a 2.0 petrol and the pump cost was about £24.
Recently I had the cambelt changed on my 99 Pasat TDi at VW dealer and I requested the water pump to be changed at the same time, VW charge £26 + VAT for the pump, PART NO 028121004X, very reasonable I think and most VW/Audi models from 1997 on use the same pump.