As much as I liked the look of Lightroom, I went with Bibble for RAW and am close to going with PM.
Truthfully, PM seems like a high price to me for just one part of the work flow. While the tagging seems to have improved here, Lightroom is a big step ahead in keywording.
Specifically:
* drag and drop in many ways -- keyword onto image, image onto keyword, one keyword under another
* hierarchy of keywords and the ability to rearrange
* viewing across the library of keywords (i know this is beyond the scope of PM)
* autofill of keywords
* when the keyword panel is active, the numbers 1-9 become the shortcut for the most recent keywords used.
I think PM could copy a few things from LR in this area.
As others have said, if PM had a lean library function, it would be a slam dunk! I know (hope) its coming at some point.