I disagree that they're useless. They seem to me like they stay for longer than a second-- I don't know if they really do, and I don't think they last for two seconds, but they're there long enough to be noticed a lot of the time. It also seems like the X fades and a second or more later the name fades, so there is a marker there for a little longer. It's helped me in figuring out where enemies are and what my team's doing. I'd like if something showed this information if you're looking away; IIRC Halo 3 would put a little red triangle close to the edge of your view pointing to any Xs that weren't in front of you, which would be nice. I'm OK with what we have now though.