Constantly! I have alerts set up, but if there's an item that I really really really want, I usually check on it when I'm on the site.
For example, a few weeks ago I was just poking around the site and decided to do a search for "Randy", which had been on my wish-list for years (but was often out of stock for the color I wanted). When I searched, it popped right up, in stock and the correct color! I bought it on the spot.
A few hours later, I got an e-mail letting me know that the product was back in stock. :op Too late, already ordered it!