Since 1.3.1. While vanished if you walk around someone they can hear you walking. Meaning they know you are there.

Using newest recommended build 1.3.1 r2 with newest vanish.

Bukkit problem. I suggest flying until it's fixed.

I've committed code that handles this problem. Waiting on final review and being added into CraftBukkit

This was resolved in the latest dev build.

I have the same problem. I vanish and teleport to someone to see what they're doing, and they can hear all of my footsteps and get pushed by my player, so they know that I'm there.

I was going to report this problem too.
It's like bukkit is predicting that players will be moved based on the pre-1.3 players-can-get-pushed-by-players mechanic. I'm probably wrong about that though

just found another sound bug while in vanish. we thought the footsteps bug is still active, but it's kind of another one now.
we can reproduce it without problems. how: the vanished guy walks through a player and this player hears just a short step in the exact time when the vanished guy hits the other. walking around the player does not play any sound.
the big problem: you can also hear this single step when the vanished user is flying, confirming its not a real step, but the collision. If the vanished guy is now waling around within the player, the player hear's a lot of "steps".