I have a few times. Slow from Hong Kong. Picked up a 30mw laser before the ban, and a 900 lumen light and about 10 or so Romison and Ultra fire cree lights. One of the Ultra fires died.
Good value, I would not rely on the stuff for 1st tier.
I have a few things on order with dealextreme right now.
Have used them about a dozen times in past.
Borderline quality on most things.
My current way of getting cheap stuff is to find it on Dealextreme and then check eBay/supermediastore/mertline as well. At least with eBay you can build up your member rating.
I've purchased several times from DX and had pretty good luck. Like everyone says, shipping takes a while from Hong Kong, but the quality is pretty good for what you pay.
I got several lasers and such from them - everything correct and everything works as advertised. Check the reviews - that will give you a good idea on quality.
I have 2 sights ordered from them right now. The knockoff EOTech and the knockoff Trijicon.
I've bought from them many times in the past. Shipping can take a while if something is not in stock, but it's not bad if it's in stock considering the ride from Hong Kong.
To be happy with your purchases from Deal Extreme, you have to have realistic expectations. Their multitude of off-brand and no-name flashlights often will produce ridiculous amounts of light for next to no investment, but very few I've acquired have lasted very long (they just quit working). They're fine for utility use around the house, but I would never depend on them.
The drop-in LED modules I've acquired have been very successful on my end. I've had a few that didn't work, but those that did initially have proven to give good service and I'll continue to use them to upgrade SureFire products. You may have to try a few to get one to work in a specific light due to tolerance issues, but that's not a problem in my opinion given the price.
Some of their promo stuff can be good deals too. You can get a bag of the little keychain LED lights that are brighter than the Photon from which they were cloned. They're less expensive than buying the batteries for them, so you can't really lose. Almost all of mine have worked well. When the batteries die, toss it and get another.