There are new FTC guidelines for bloggers who review products that are provided to them by companies. (Click here for an overview.) Basically anytime bloggers review products that they have received for free, they need to state it upfront and early on.
I don't know if you can call what I do reviewing (I guess it is? I mostly do comparisons and swatches), but you should know that I almost never receive stuff for free. (The only time I receive products to review are when I'm writing for Painted Ladies - and I always disclose that in my post, and I only share those reviews on my own blog as a link.) Um, yeah, the (sad) truth is that I buy all my stuff myself, or I receive them as gifts (PERSONAL gifts, like for Christmas) or I review free samples that get tossed into my Sephora bag.
No one pays me to do anything, makeup-wise. I'm small potatoes, my friends :) I try to be as objective as I can, although if you know anything about me, you know that I am inclined to love anything Urban Decay just because it IS Urban Decay, and they are my favorite.
So yeah. That's all. Just so you know. Even though I'm so small I would totally fly under the radar, if a company decides they want to send me things to review, you will know it.