You'll have to get very intimate with your database, particularly your Events table, but you should be able to tie in events against Nodes.
As an example - if a box reboots more than once a week (untested, but the DB query works..)
Type of Property to Monitor: Custom SQL Alert
Set up your Trigger Query: Node
Nodes.NodeID IN (
WHERE NetObjectType = 'N' AND EventType = 14 AND EventTime >= DATEADD(DAY,-7,GETDATE())
GROUP BY NetObjectID
HAVING COUNT(1) > 1
EventType = 14 is the reboot code (see the EventTypes table for a list)
DATEADD(DAY,-7,GETDATE()) calculates 7 days ago (i.e. in the last week)
NetObjectType = 'N' pulls only Node events
HAVING COUNT(1) > 1 for those that match more than 1 time (adjust accordingly)
Thanks Andy -- that query works great. I'm having trouble getting my alert to actually trigger, but at least I know the query portion is good.
I know this has been answered above by a really complicated 'get intimate with your database' answer but why wouldn't you just have the event (I.E. Last boot time changed) send a trap to your poller and alert on that threshold?