(Its the option labeled "Null votes" under Miscellaneous)

I think what's being suggested isn't so much a null vote that is actually cast with a total effect of zero on the node and -1 on the votes available to the caster (my understanding is that this is what's currently implemented) but an undef vote that is not cast, with a total effect of zero on the node and zero on the votes available to the caster, so that one mistakenly clicked vote won't require reloading the page to cast other votes.

I've had just the situation described in the original post, where I'd clicked five or six votes into a long thread, then clicked one on which I didn't intend to vote. To clear that vote, I had to reload the whole page.

This is a valid concern--is there a better solution?

I think what's being suggested isn't so much a null vote that is actually cast with a total effect of zero on the node and -1 on the votes available to the caster (my understanding is that this is what's currently implemented)

Nope, the "null" vote is just that, no vote at all. No decrease in your available votes and no effect on the post's reputation. Its as if you never voted for that node.

Of course you could actually enable the option to understand the behavior thoroughly && firsthand but maybe a better description would be helpful as well:

The null option provides another voting option (in addition to the default ++ && --) for each node. This new option is labeled +=0 && actually exists as a "checked" radio button within the HTML so when you accidentally select a value altering vote option, you are free to re-select the default +=0 radio button so that no vote (on that node) will be cast when you proceed to the "vote" stumbit button. =)

Hope that helps a bit. I remember asking for this feature way back when... gosh... that must have been like 6 months ago. Sheesh. I still find it mighty handy. TTFN.

-PipTigger
p.s. Byslexia is a Ditch!