I think v_r_system still relies on heartbeat... but whatever.
How about this:
http://smsug.ca/blogs/garth_jones/archive/2008/02/22/location-of-last-logon-user.aspxor check out Garth's argument about v_gs_computersystem:
http://smsug.ca/blogs/garth_jones/archive/2007/03/22/224.aspxbut John Nelson argues for v_R_system_valid.
and different people might argue that neither v_gs_computersystem, nor v_r_system_valid are the optimal places, you should rely on the Console Usage reports to get the best "who does this pc belong to" correlation.
I like to offer people Garth's Location of last logon user (the top link of all potential locations) and let you decide what you think is the best location for your environment.
Standardize. Simplify. Automate.