For me, the answer is yes and no.
45 seconds per post. At the time of posting this, 11862 x 45 equals at least 533790, divide that by 60 and you get 8896.5 minutes.. or is that hours (?) spent on PC, figured out just by post count. Then add up all my other posts in forums that posts don't count in, specifically member fanclubs and other trivia, and the amount of time on PC gets boosted. Then think of all the time it takes to think of posts and read other posts... yeah, basically post count helps measure time spent on PC, so in that aspect I find it important. But lets do further maths. November 15, 2005 -> today = 1159 (that's going by 365 days in a year) then divide that by 24 hours in a day. And you get... a recurring number? Okay, working it out that way isn't going to work. But the point is, post count does show how much time you've spent on PC from the time you joined, so therefore, it kinda shows your loyalty to PC, or however long you were allowed on... okay, I'm giving up on this point.
However, ignoring all the stuff I just said, post count doesn't matter anymore, because once you're in the top 10 posters, it's really hard to move up a position unless you post in every free minute you have. Logically, people with post counts between 2000 and... 7000 (?) would care more about post count (for those who are competitive with numbers, that is) rather than anyone who's higher up in the post count positioning.
Though for those that aren't competitive... quality matters more. That's kinda why I post in OT most of the time because the posts don't necessarily have to be of good quality, but just to have fun. In the past, however, I became obsessive for short periods of time (early October last year, but the aim was just to get to 11k, then there are other shorter periods of time, that don't stand out in my memory.) Even from the start, I was posting lots because I thought that post count would make a difference in popularity, as people have mentioned. Nearly 100% of those posts were bad quality because of my competitive nature took over and I posted things that weren't even related to the topic.
So yeah, half of that probably doesn't make sense, but the answer is basically... used to be yes, and now no.