Uptime and performance monitoring service Pingdom has done a study of social network uptime in 2008. They looked at some of the more heavily-used sites – Facebook, MySpace, LinkedIn, Twitter, Friendster, LiveJournal, Orkut, Bebo, Hi5, Windows Live Spaces, Last.fm, Classmates.com, Reunion.com, Xanga and Imeem.

Twitter and LinkedIn experienced the greatest amount of downtime in 2008, but the study reveals a lot more interesting detail.

Their key findings included these “standout facts” and trends for 2008 include:

Only 5 social networks managed an overall uptime of 99.9% or better: Facebook (99.92%), MySpace (99.94%), Classmates.com (99.95%), Xanga (99.95%) and Imeem (99.95%). Again, it should be pointed out that Imeem was only monitored from May 9 and onward while the other sites were monitored the entire year.

The single most massive social network incident in 2008 happened to Friendster. The service had a data center outage in November that caused more than 23 hours of downtime in a time span of less than 3 days. If it weren’t for that incident, Friendster would have placed much better in this survey.

84% of Twitter’s downtime happened during the first half of 2008. July and onward has seen a big improvement in site availability for Twitter.

77% of LiveJournal’s downtime happened in Q4 of 2008. It is too early to say if this is indicative of a trend or if it was a temporary lapse in uptime due to the service’s migration to a new hosting provider.

LinkedIn’s downtime has been increasing over the year. Each quarter has seen a larger amount of downtime than the one before it.”

The full report is free and its .pdf can be found here.