I pin if it's a small quilt, but anything larger than 40x40 inches, I spray baste and it is the absolute best! I've done queens and kings and had no issues. The example that was given above on how to do it is exactly how I do it.
I've washed them all in my machine and had no issues with the spray coming out.
You will LOVE it. Yes, it can be expensive, but shop around. I use the 505. I'm in Canada, fabricland charges an arm and a leg, Walmart had it for almost 1/2 the price!