The main blog does have ads, as does the forum (bottom of the page for both). Do you have an ad blocker turned on?
That aside, yes, I suspect a majority of the income comes from affiliate links. Most, but not all, of the stuff on the "MMM recommends" page are affiliate links. Personal Capital, for example, pays $100 per referral that signs up and connects accounts w/ at least $100,000 in assets. Given the huge traffic this blog gets, I am sure there are a fair number of those daily.
Obviously, MMM is by far the exception in terms of profitability, rather than the rule. My blog also has ads and affiliate links, but as my traffic is quite low, especially compared to MMM, I have been making about $100 a month in the past few months since I started. I cover how much I make in each month's net worth update, but the ad revenue is quite low. Ad income per click also increases as your page gets more traffic, so in some sense it's a chicken and egg problem.
There are a lot of blogs out there with posts about monetizing a blog, but none that stick out to me as superior to the rest. To me, it comes down to:
Writing a ton of good content - Literally nothing is more important than this. If you don't have something to say that is engaging and different from what everyone else is saying, you're unlikely to be very successful.
Be tasteful when trying to monetize - There are a lot of sketchy bloggers out there that recommend services and products that are actively harmful to their readers goals. This really bothers me. Heck, it even happens here on this forum. Lots of people arguing strenuously that objectively inferior services are better than low cost ones, and when you click the blog link in their signature, you learn why. Be ethical.
Engage everywhere - You've got to be on Twitter, Facebook, Pinterest, forums, and everywhere else you can possibly be. Be helpful and decent, and develop real connections with people. Those who you affect in a positive way will be the ones who retweet, pin, and share your content, increasing your audience.
Obviously it would be easy to discount my opinion since I don't make that much from my blog, but these have been the key to my slowly and steadily growing readership. It's also an approach of integrity, which is important to me.
