I use Lightroom extensively for both adjusting the exposure/contrast on my images and then adding titles, descriptions and keywords to the images. My approach to keywords is to generally get a common set of keywords that are the bare minimum for a batch and then go through each image in turn and add specific keywords that describe that image. The problem - sometimes I go over 50 keywords, and when I then upload to my 20 or so sites, I have to fiddle about removing keywords from some of the sites before I can finish the uploads. There is a further little issue on some sites in that they accept compound words as one keyword on upload, but when you are above the limit and start to remove the surplus keywords, the compound words suddenly count as individual words again.
Lightroom doesn't have a way of counting keywords, but I found a plugin that does allow you to check if you are under 50 keywords.
http://www.lightroomforums.net/archive/index.php/t-13537.html?s=a1d0c56268d256cb4b001cc484cb1370 and have written a more detailed explanation on how to use it (if you have this issue) on my blog at
http://www.backyardsilver.com/2012/07/how-to-count-the-number-of-keywords-in-lightroom/Hope this helps the Lightroom users among you.
Steve