No...it wrote into the .xmp file (or the xmp bock in the case of DNG) only. If you toss the .xmp file the raw file is still absolutely untouched...what the bug was causing was problems in the database record of the file...not the original file at all.
You may have been confused abut an earlier version of Capture NX actually writing inside the actual raw file and that bug resulted in the raw NEF being corrupted...
I'm sorry but, as the result of some research, I must respectfully disagree.
First, for LR version 1, here is a direct quote from Victoria Brampton's "Missing FAQ" book, page 164:
"In version 1, for proprietary raw files, most metadata is written to an XMP sidecar file, however, the updated capture time is written back to the raw file itself, changing the modified date of the file."
"That shouldn't cause any problems as it's only written to the metadata file header, and doesn't affect the raw image data itself, however it is a point of concern for some people who they[sic] feel that the raw files should never be touched in any way."
As to the bug in version 1, here is forum thread discussing it:http://forums.adobe.com/message/1454773#1454773
Now, for LR version 2, it looks like there are two modes. The next paragraph in Victoria's book is:
"For that reason, in version 2, there is a setting in Catalog Settings > Metadata panel to allow you to choose whether the updated time is stored only in the catalog, exported files, and XMP sidecar files, or whether it can be updated in your original raw files."
So, considering Michael's original statement of:
"Lightroom never touches the original raw file. All edits are virtual."
I think a fairer statement would have been:
"For LR V2, the original raw file is never touched, with the exception of the case of changing the metadata capture date of the photo when you have the appropriate mode set in the Metadata panel. (For LR V1, changing the metadata capture date of the photo always changes the original raw file.)"