Matteo: Frankly had not noticed a big difference. However, if my experience is any indication, there is a definite life cycle to an individual's interest in and participation in a forum. I have gone through this cycle on several forums, most notably the Continuous Wave Boston Whaler Forum and the AOL Weightlifting Forum.
1. Discover the forum. Read it eagerly. Learn the ropes.
2. Begin posting, usually rather extensively since the forum subject is one I have an active interest in.
3. Learn who the old-timers are, who has true words of wisdom and who are pretenders.
4. Maintain an active participation until suddenly I find myself in danger of getting repetitive and boring. Start to limit postings to those topics on which I believe I have something of value to contribute.
5. Realize that I am now one of the old-timers. Begin to deplore how the forum is declining, when in reality it is just changing somewhat because of the turnover of participants. Change is inevitable in any human endeavor.
6. Start to just tune in occasionally to see if anything new is going on.
7. Occasionally notice it on my favorites list and wonder, "why don't I go there anymore?"
Now I don't expect this to happen to me on the Busse forum, although I find myself reading more and posting less these days. The key to me in the above list is to realize the "change is inevitable" thing. It isn't necessarily better or worse, it has just changed somewhat from the old familiar.
At least we haven't turned into old grumps who tersely refer all newcomer questions to the search function, like folks on a lot of forums do.