I have tried it. It's ok I guess, but it doesn't seem to be able to block flash-ads - which makes it kinda crappy, since flash-ads are the most annoying.
Pithhelmet blocks flash just fine. You can also block flash-ads in CSS, but only in Firefox/Camino/Mozilla/Netscape. Safari can't do this for some reason.
Netsentry is way faster than Pithhelmet, though - and it's easier to set up than CSS. So, if you can live with flash-ads and don't want to use CSS (and can live with an extra window on your desktop), I'm sure you'll be happy with Netsentry.