A questionc came up today regarding heartbeating in OpsMgr 2007 - specifically, whether we can easily group systems and deliver missing heartbeat notifications based on specific computers and teams that manage those computers. The answer is yes - but the process of heartbeating and setting this up is different in OpsMgr 2007.
Heartbeat monitoring is handled by the Health Service watcher node (RMS/Management servers). The watcher nodes expect heartbeats from agents - if they don't get one appropriate rules will fire to indicate the problem. This works perfectly because, like in MOM 2005, heartbeat issues must be detected at the management server level.
Splitting out systems so that notifications can be sent based on computer group membership is also fairly straight forward - just create a new computer group whose target is 'Health Service watcher'. The further criteria for the group can be whatever expression you need to uniquely identify your systems – simple pattern matching/wildcarding or full regular expressions. From there, you create subscripts for alerts generated by systems in these computer groups and the problem is solved! More detail is available in the PSS teams blog at http://blogs.technet.com/smsandmom/archive/2008/03/25/opsmgr-2007-monitoring-health-service-availability.aspx