I used extensively worn down skate shoes for PK at first, they felt fine, they had no grip on the shoe, although i could grip better than others who had big grippy shoes somehow.

But I decided to buy some Nike Air Pegasus due to fear of getting knne/ankle problems from not having shock absorbing shoes. Firstly i felt like i was walking differently, everything felt too cushioned and i could walk alot more quieltly in my skate shoes. I tried doing all the things i usually did in my skate shoes.

 I had less grip/found it alot harder to grip properly. Wall-runs were much harder. Balancing was badly effected due the all the grip on the underneath of the shoe.
 Landings felt slighlty heavier, didnt feel right, and also they sounded much heavier.
 When running on a treadmill, i felt that i was running differently, even the gym instructor said i was running wrongly. And ive never had problems with running properly.
 Overall i felt that i was restricted, and that i could not use my feet properly.

When i switched back to my tatty old skate shoes, i could balance no problem, felt like i was walking properly, my landings had to take a teeny while to adjust back to normal, and grip was a million times better. I think that grip is not too important on shoes (unless it is wet or something), and that its the way you use your feet that enables you to grip better.

Heh. I just bought these: http://www.evolvesports.com/PSYCHE.htm. You can't beat $19 shoes with climbing rubber, especially since I'm just starting out. Evolv is a really good climbing shoe manufacturer, too, quite reputable.