I have been participating on a lot of forums and communities to promote our new app.
Not all those forums support centralized commenting system like disqus.com.
I am sure this is a common problem faced by people participating in multiple forums/communities.
How do you all ensure that you are notified about any new comment in response to your posting or a response to your comment? Is there a desktop tool or a web tool?
Many places now offer RSS feeds of a single post including comments (such as this site) or even just the sites entire comments feed (blogger) depending on the size of the site.
Just subscribe with an RSS aggregator and read over the feeds daily.
One easy way, but not necessarily the fastest, would be to sign up for keywords about your product/web site with Google Alerts (http://www.google.com/alerts)
Basically on a daily basis Google will email you with links that mention your product/site. So as long as the forums are open (do not block search engines) you should hear eventually that someone made a comment.
The downfall is that if they don't mention your product/web site you won't be alerted.
Hope this helps.