I'm a little late to this debate, but I for one absolutely love LR. I use it in conjunction with CS5. I've used Photo Mechanic for several years, but I've mostly phased it out (it's great for reviewing and culling images, but that's about it).

I used to edit images one photo at a time through Photoshop, which would take me about one hour for ten edited photos. Now I use LR to create global adjustments for a series of RAW images. I can do about 100 an hour, and the results are much more consistent since I can see all the images in one place.

I use LR for basic color correction, white balance, tonal and exposure adjustments, dust removal, and light dodging and burning. After that I'll bring the image into CS5 for advanced touch up (Content Aware retouching is AMAZING) and sharpening.

I also just figured out how to use the catalog to organize my entire archive, and it's great. I haven't had any problems using an external HD.

I learned LR through some free online tutorial videos. There are a ton of them out there that you can find with a quick google search.