I'd argue that freemium works best when the "premium" part has value for the user. But, making money (i.e. directly contributing to revenue/profit) is just one way to have value. Saving time is another.
So, I pay DropBox not because it helps me make money, but because it's worth the savings in time and frustration trying to come up with an alternative.
Many of the most popular freemium products have a price point that is low enough that large numbers of people can easily justify the price, if they actually use the product.
This is in contrast with Evernote and Dropbox, both of which I use for free but neither of which I plan of paying for in the future. They work well enough for my needs, and if I grow out of them, I'll probably just either cut back on my use or try to find another solution. Maybe that makes me a freeloader or cheapskate, but I imagine I'm not alone.
So, at least in my case, Freemium works best for products that either directly or indirectly contribute to making money.