One advantage to studying Usenet is that since it's been around for so long, it's easy to get historical data and say something about its evolution. Furthermore, it's easier to call what we know of it a "community" (although we're still forced to sample it, for our purposes), whereas we never really know if we've crawled*all* the blogs.
What we have done so far is obtained data since 2003 for 200 newsgroups with "polit" somewhere in the newsgroup name. Here's some over-time behavior, a plot of number of posts per day, and number of hyperlinks (in original, non-quoted content) per day:
Posts and Links for All Political Newsgroups
This is a smoothed version of the data, so to illustrate a general trend. The first thing you'll notice is the bump in November 2004, which we can attribute to the US Presidential Election. The next thing you'll notice is that while the number of posts is declining, the number of links remains stable.
Here's the same data for a small subset, can.politics:
Posts and Links for can.politics
Predictably, the "USA Election bump" doesn't hold for all the groups. For uncultured folks like me who had to look it up, the last election in Canada was January 23, 2006. We do still notice an increasing tendency to link, per post. Perhaps people on Usenet are going more to outside sources. Or, as another intern put it, "They're getting lazy."