Saw System Sessions posted on the PSS blog and it shows an example of information being written to the error log as 'spid5s', where the trailing 's' indicates a system session (spid). You can also filter them out of the processes by doing this:

select * from sysprocesses where spid < 50" you should use "select * from sys.dm_exec_sessions where is_user_process = 0"

Not a huge change, but using spid < 50 always seemed like a hack. We'll never have more than 50 system spids!