Pyramid plunder still is the best place to train thieving, but this one seems to be very good for collecting herbs. I collected 10 herbs from the summer garden. One of them was guam and the rest were ranarr or higher. Going quickly you can almost collect four herbs per minute.
That experience has been there since RSC, so it's nothing new. The level-ups have some odd formula, but a very accurate estimate is doubled xp = seven levels.
Here's a little video clip I made for the summer garden, under 40secs from the gate to the tree. http://www.netikka.net/orccu/Garden_summer_by_Orccu.wmv
Being the level I am, there are not that PK'ers for me at the abyss. It's probably that most of higher level people realize that they could make three times more profit by runecrafting, not abyss pk'ing. (Of course there are exceptions, too.)