I see it this way: if the topic is about your webpage and you can add something valuable to the discussion then go for it, but see it as a way to build an audience and not so much links.

Even if the links are nofollowed or not indexed at all: nofollow-links are essential to a "natural" link profile, as most websites do have a number of nofollowed links (and even links from noindexed pages, which google crawls and "sees" nevertheless).

Low hanging fruits are usually common errors/mistakes someone made. So for starters I would do the following thing:

Register with Google's webmaster tools.

Crawl your site with xenu's link sleuth (google it, its freeware).

• Look for 404s -> fix them
• Have a look at all titles of  you page: are they unique, short and do they have the important keyword in the beginning.
• Look at the depth of your page. Anything above 4 should be looked at.
• See whether all pages send the right status code (404, 200) and the right charset
• Analyze one page with Google's Pagespeed Browser Plugin, fix whatever comes up

Adding to Ryans post:
The amount of links is one thing to consider, but also consider the depth of your site, that is: how many clicks does it take to reach any given page. Use a crawler like Xenus link sleuth and crawl your site. You should look into anything over 4 or 5, depending on the amount of pages.

For an ecommerce site i wouldn't worry about the 100 links per page warning, but 200 visible links are too much. Best thing to do is too look at every object of a page (links, images, buttons, badeges etc.) and ask yourself whether it is really necessary or dead weight. Reduce as much as possible.

Nearly forgot to ask you: are you using some sort of social media widget? These little buggers sometimes contain links to tons of sites, thus increasing link count. There used to be an addon for firefox called link grab! which printed out a list of all links on a page.