I have a site that I have the PayPal IPN working fine on. The only problem I am having is that I did not know what to set the database fields at for each field. I basically have everything set at nvarchar(50) in SQL. Here is a list of all the different forum fields I found out that "could" get sent thru
I want to use this service, the only issue is that they only work in other currency to Australian, and it doesn't look like they are going to do Aus support soon.
Apart from that, the IPN guide helps heaps as HuwR said.