Since Lightroom's colorspace is based on prophotoRGB but has a different gamma, you cannot use any of the published values for the color patches in one of the Gretag MacBeth colorcheckers that many people use to check the color rendition of their toolchain and that you can use to calibrate the color rendering of ACR for your specific camera. Usually you would do this in ACR/PS, but if you only have LR, what do you do? Well you can use the below values in Lightroom and do it manually by going back and forth between patches and changing the hue and saturation in the camera calibration part of the develop module (after white balancing on the second grey patch!). These values are based of the values in this excellent page, so there will be a small error in there of about 1%. I simply did the appropriate transform to gamma 2.2 for the values in the ppRGB column. The values are in percent of the channel in R,G,B laid out just like the colorchecker chart.
Honestly, I have no idea why not all the grey patches are neutral, but this should help those manually calibrating in Lightroom.
EDIT: No idea why, but blogger messes up my HTML table, so it is now just a picture of a table. Hope this still works.
UPDATE 9/19/07: I uploaded a table with more precise values from 16-bit values of the colorchecker reference in the next post.