jQuery adds padding for browsers that don't support certain features or have certain quirks (yes, IE, we're mainly looking at you). This is overhead that will slow things down.
That being said, if you can afford to develop for modern browsers only, then by all means, use plain JS.
(Same applies for other, non-UI-specific JS: Need Array.forEach()? Use it. Define Array.prototype.forEach() for legacy IE, rather than piping all browsers through "MyLib.forEach(myArray, function(item) {... })".)
and i certainly don't want to do the work of figuring how to sidestep incompatibilities that _are_ present.
even if the distastefulness of _that_ was half as bad, i would still rather make my users "wait" for that 37k.
again, that's _me._ not telling anyone else how to do it.
-bowerbird