Microsoft still recommends 15 characters or less.
If you give a recent computer a name longer than 15 characters, anything more recent than Windows ME/NT 4.0 will be able to talk to it using the full name. Older than that and you need to truncate to 15 characters. When you are setting a computer name, if you go into the “more” button it will actually show you the NetBIOS computer name if it differs from the standard name.
Here is a KB article on the different limitations for computer naming:
http://support.microsoft.com/kb/909264
Also, here is the Windows 2008 R2 computer naming recommendation:
http://technet.microsoft.com/en-us/library/cc731383.aspx
as you can see, still 15 characters.