[Nadr]

I inspected the source code of competitor and discovered a commented line like this:

<!-- KEYWORDS & PHRASES -->

Also, further down the page I discovered tons of links with keyword stuffing that were using a foreground colour almost identical to the background colour.

What should I be doing?

[shabbir]

Report it to Google and if you do not do that also then also they would not get bigger with these techniques in Google

[phcarmaster]

This kinda of strategy is for short time. Google will eventually see this and penalize your competitor.

[yohan]

Google, somehow will know about it and they will give penalties on this sites/blogs or even worse they might be banned..