I've been carving pumpkins for years and years, and have my technique pretty much down pat. Since my family does an insane number of pumpkins each year, I do get a lot of practice. Unfortunately, some of the techniques that lead to an amazing pumpkin carve are actually pretty harmful in stamp carving (I have an unfortunate tendency to undercut all my carves - and I have almost no ability with the lino/wood cutters).
So far, I've been carving with Speedball's Speedy Cut (don't mind it, but have a sneaking suspicion that my stamps shouldn't be... degrading?... so fast) as well as erasers from the Dollarstore. If they weren't so convenient to carve with - and didn't smell so nice (who knew?) I would never use the erasers. They are very tough to work with. Neither of these two mediums allow me to do any detail work - I just can't get fine lines or tiny flecks. It's likely my technique, but I've got some different carving mediums on order from Stampeaz... I'm excited to get it and try them out. Find out what I like and then order some more... As I said, addicted.