A new report by Perseus has some interesting statistics:
Weblogs updated less than once every two months: 66%
Weblogs updated once a day: 1.2%
Active blogs (as defined as those which are updated more than once every two months) are updated on average every 14 days.
26% percent of weblogs created are never used more than once.
Weblog freshness, like weblog linkedness, follows a power law, something that is important when designing a weblog aggregator, see: ‘Blog Metrics’.