I have file drwtsn32.log with size 6GB, located in directory:C:\Documents and Settings\All Users\Application Data\Microsoft\Dr Watson
It is save to delete this file.
Here is little trick for avoid such long file. Select Start, All Programs, Accessories, System Tools, System
Information, Tools, Dr Watson and verify that the box before "Append to
existing log" is NOT checked. This means the next time the log is
written it will overwrite rather than add to the existing file.