There is a new affiliate network monitoring service from Nickycakes.com called Network Uptime that sends alerts when an affiliate or CPA network goes down and back up.
For as long as I can remember, affiliates have been tormented by downtimes and their impact on earnings, so this is a useful service for the affiliate monitoring their campaigns.
Most of the downtimes seem to be a matter of minutes, but there have been some extensive outages tracked. A cool thing about the Network Uptime alerts is that you can see if a particular network is routinely going down.
More details at http://www.nickycakes.com/affiliate-network-downtime-alerts/.