Firstly, I should state that I have had zero problems with this device performing its intended duty. I do, however, take issue with Apple charging me £15 for this adapter. It should also be noted that this is DVI-D (digital) only, so a passive DVI-to-VGA adapter on the end of this thing will do nothing. If you want to be able to hook your Mac up to a VGA port as well, you will also need to get the VGA equivalent of this.
Secondly, the size is not ideal (though unavoidable). While the small amount of cable is needed to get the bulky DVI end away from your USB and ethernet ports, it makes the whole thing rather big, which on my short desk can be a problem. Often, not being able to rest the whole adapter on the desk, it starts to bend or pull its way out of my Mac's Mini-DIV port.
These negatives aside, you don't really have any choice. If you need one, this is the only thing you can use, and like I stated at the beginning, functionally it is perfectly competent.