See for me, hmm, this is hard to explain.
I find that real curse words interfere less with my immersion. I get that frag and drek are very shadowrun. It's cute, and I'm nostalgic about it. But if I'm really in character, having to say frag and drek instead of the real thing kind of pulls me out of it, pulls me out of the dark, gritty, tough world that SR is and making me feel awkwardly like I am in some kind of kids' show.
As the poll shows, I'm in the minority here. : )