I get the same thing too. Don't quote me, but it "seems" to correlate to how much Facebook email messaging you do with the person. For example, one person I have recently chatted via Facebook email alot to is showing up most often there for me even though I don't really look through her picture galleries all that much. I do view her page "alot" in comparison to alot of other people on my friends list, but I also view another persons page alot and hers don't show up as much there for me. They do show once in a while though, possibly because we've had a couple of Facebook email chats recently, but not as many as the first person I mentioned.

So my guess is Facebook somehow checks the percentage of email correspondance you do with people and shows the suggestions accordingly. Or at least, that somehow possibly also figures into, it amongst other things.