Using the HH

I've noticed one decent advantage to online play compared to live play is that when someone mucks a hand in a showdown, you can see what they had even though they didn't show. Has anyone else noticed this and used it to their advantage? You can see how ur opponents play certain hands from certain positions...

Yep. Use it all the time. You'd be a fool not to.

the showing of cards at a showdown is a local ruleing in poker some sites have it some do not, personaly i think it should be a permentant ruleing as people would allways know if there tryed a steal and lost there hand would be shown, it would put off alot of over agg. plays at low levels

it's a general poker rule too. if a hand makes it to showdown a player has the right to ask for the hand to be shown regardless of muck... this is horrible ettiquette if you do it in a live game and would really piss of the losing player.

With that said, I do it all the time online to get an idea of what the losing player's range is

Not all sites do this and I've yet to play at a B&M that forces the show if a player requests. I play primarly at FullTilt and they do not show the mucked hands.

Edit: Its also important to remember that when your bluff goes sour, assume that table knows exactly what you bluffed with on those sites. Just another perspective to look at.