Lightroom 3 (I am using 3.2 RC) has some superb rendering nowadays. Lots of detail, pleasing grain behavior, great noise reduction and more. I am generally very happy with it. There is one area where it can use more work and I am not the only one to think that. I ran into this again recently in the below shot of a glassblower at a county fair. If you mouse over this image, you will see the rendering of the same raw file that is obtained from Nikon's capture NX. Pay attention to the flame.
Mouse over this link to see the image using the Adobe Standard profile
Clearly, Nikon's capture does a far better job creating a smooth transition in the highlight area of this image. The Lightroom version has two ugly posterized step transitions in it. Clearly it is not dealing well with areas that are blown out in one or more channels of the raw file. If you try different camera profiles in LR, you will get different highlight posterization but none as good as the Nikon Capture example. This is also often observed in images of setting suns and such where you will often see a weird halo around the sun. This is the same thing as was observed in the article I linked to above.
Of course, I would not want to do lots of work in Capture NX as that program has a horrid interface and I do not always like the color rendering, but clearly this is an area where Lightroom/ACR could improve.
EDIT: I added a mouse over link to show the image when using Adobe's Standard profile. It is better than the other profiles Adobe offers or one created using the profile editor or the Passport software, but it still does not do as smooth a highlight as Nikon's software.
EDIT 2/5/11. This issue has now been fixed by Adobe.