Heard alot about this but have never done it on any of my recent pairs of gloves, I find that long term there is better grip and the durability is greatly improved. (I wear either Adidas or Uhlsport)
Night and day difference in grip for me after prewashing. I had never heard of it before reading about it here, but even back in the day I could tell that gloves right out of the bag were not at their best, so I used to train in new gloves once or twice before using them in games. I called it "seating the grip."
Lots of posts about this already ...
For starters ...
http://theglovebag.com/forums/p/1788/5573.aspxhttp://theglovebag.com/forums/p/8281/30964.aspxhttp://theglovebag.com/forums/p/7592/27911.aspx