I use two techniques to say on top of these sorts of things.
Most forums in which I participate have a "follow this discussion via e-mail" function, and I've got a number of gmail rules set up to direct that content to specific folders. In cases where there isn't a mail function, I'll use a hyperlink pasted into my gmail calendar as the reminder.
Now, a bigger question, which will lead to whether or not this method works for you or not is about WHY you're using the forums. For me, forums are not a critical part of my communications, nor do I consider it a bad thing to post a thoughtful quality reply after a day instead of stressing about being the first useful accepted or upvoted answer. Those may be important to you, in which case you may want to tweak the following.
Specific discussions that I follow (the long-running type) usually get their own e-mail label. Topics and boards I follow may just get a label like "Stack-Exchange" or "SE-Productivity". "Check forums" is a task on my to-do list that is a "nice to do" but not critical to get done, so when I have a break or need to redierct for a few minutes, I perform a quick triage on the e-mail inbox folder for forums. Don't need to reply? I just delete it. Quick reply? do it and get it out of the way. Need time to formulate a post? I block off time in my calendar to do so...with the understanding that if I can't get to a reply in time for it to be relevant, this may end up turning into "Don't need to reply." I also keep in mind that sometimes, while my answer may not be the most timely, its relevance outweighs the delay in getting it into the discussion. Like everything else in my to-do list, I set a fixed time to do this triage...sometimes ten minutes, sometimes an hour.
Periodically, when I get to a "review my productivity" task, if my backlog of forum duties is getting out of hand, I need to re-prioritize my participation in forums, and save/delete/reprioritize the list of forum to-dos appropriately.
The biggest thing though is to balance forum participation against the value you place on that participation. Determining this will make it a lot easier to prioritize, sort, and schedule those interactions in your life.