The Double Layer LightScribes only do 2.4x while most these days do 4x. Some are said be on the way that will do 6x. 2.4x vs 4x for double layer isn't really much of an issue at all in terms of speed.
As for +R and -R, the recorder does 16x for +R and 8x for -R.
I have teh external model which sells at newegg for just $134. Considering it comes with a FireWire/USB case, and the drive, it's better than a fair value even without teh LightScribe function.
LightScribe uses a coated a disc surface in conjuction with the hardware's laser to create a gray-scale "scribed" surface on the media. That means you must buy LightScribe surfaced media. It's about $18 for a package of 30 CD-Rs, and about that for a package of 10 DVD-R 8x DVDs. So the media cost more. You can use any media you want mind you. You just can't scribe it, unless it has the LightScribe surface, and that's what you pay extra for in those media prices.
It can burn simple text labels in a couple minutes, but an entire surface can easily consume 15 minutes or even 30 minutes depending on the speed of the write; 1x or 2x.
I bought one because it was so close in price to a regular drive, I thought, what the heck. It's just an additional feature to have, even if you rarely use it.