I think the reasons why I enjoy using Lightroom 3 as much as I do have already been stated by others here. It's really helpful to have practically every tool you need to edit your picture on your screen ready to be used when you process a RAW file. I just go down the list and I am done. Now I know that other RAW processors have the same type of format, but it also has a few other tools built into it that I have found useful such as the graduated filter which applies adjustments like a graduated filter would. Also related to the tools, the noise reduction is great- a little bit of luminance smoothing and color adjustment and my photos end up darn near noiseless if they need the adjustment.
I also find the organization that is built in to be very handy when it comes to locating files from different days or events. The option of adding your files to collections is a big plus for me because I can easily go through all of my photos from some event in one place and edit them the second I click the photo instead of waiting for the program to open each file separately. You can also sort through all of your photos using different filters like the shutter speed or F-stop used or any combination of the available settings.
And one last thing that I am not sure on how other programs handle it: Lightroom will "save" your editing history of your RAW files that you have started to develop. This means that if I process a RAW file, open it in Photoshop and see that one little thing is off, I won't have to go through editing everything all over again and just make the necessary adjustments, export, and get right back to Photoshop. Like I said, I don't know how other programs handle this because I went right into Lightroom when I started shooting RAW so I haven't ever really played with DPP or other similar applications.
Overall, I think it is the layout of everything and the effectiveness of all of the tools and features that have me hooked. If Photoshop had the same organization built into it that Lightroom does, I probably would skip the step of using Lightroom. Given that it doesn't, though, I will continue using Lightroom. 

