My personal preferences are a little Spartan---I usually shrink pictures to be either 4" or 3" across (I voted "small," I don't know if that matches other folks' perceptions. I just don't like them to overwhelm the text, which is where I get most of my information.
I voted "really, I just need a couple" in terms of how many---but that definitely depends on the review. If each picture is relevant, or showing comparisons, or the thing has many parts (like my Saloon Girl outfit review), keep adding pictures til everything's shown. Especially you, Lucky21, I trust you to choose useful pictures. But, like, I don't need to see three different angles of the packaging.
Also, if there are lots of pictures in number, I like to see the size scaled down proportionally.
Another note---I like how Beck usually does pictures, too---she has a bunch, from lots of angles, but she makes a collage of them all and posts them at the bottom of the review. I think that's a good compromise, because it shows all the pictures that are useful, without breaking up the words.