I notice that Slothrop's constant sexual encounters make me take him less seriously as a character. This is not just because it makes him, as my friends and I like to say, a "man whore".
Slothrop's relationship to Katje was set up as "special". That is, he seemed to really care about her and Pynchon spent more time talking about them. Slothrop even talks about missing her. Yet he goes on to have sex with anything (female and human) that moves. So this means he has a complete disconnect between sex and emotional attachment, or he really doesn't care that much. I think it's amusing that, for someone so paranoid, he doesn't really hesitate to have sex...well, I guess since it seems meaningless to him in the long run, it does make sense.
I find it curious that Greta (I think I'm reading ahead, so ignore this if we haven't read it) seems to be in the same sort of role that had been Katje's (in relation to Slothrop). That is, Greta seems like she might be there for a while, like Katje. Greta's desire for BDSM also makes me think about one sexual encounter between Slothrop and Katje, when he sort of forced himself on her and called her "cunt" etc.
I know a lot of people will probably disagree with me on this, but I continue to find the sex excessive in this book. I think I feel that way because so much of the sex is rather meaningless to the characters. It might be there just because Pynchon wanted to push the line or something...but I find that just silly.