I don't know if this also applied to the previous sound effect or not, since I never really paid any attention to it. But the click sound effect seems to be delayed by maybe a quarter second or two. As in, I press the mouse, release the mouse, wait a quarter of a second or so, and then I hear the click.

The effect should happen as soon as I release the mouse.

I tried /sndshow, and it looks like the actual audio clip does start playing immediately, but the actual click is not immediate within the file (or else the playback is delayed from when the game tells the file to play).

I'm using the 64 bit client on 64 bit Arch Linux and Alsa, if that is relevant.

Mine is instant.
MacOSX 10.7.5