Too many bloat on jQuery UI, there's an exploding, bouncing, clip, shake, pulsate animation in jQuery UI to name a few, you don't need them, there's also: droppable, position, progress bar, etc, you also don't need them.
Selectively download which ones you need, jQuery UI customizable download is user-friendly anyway, just uncheck then check which ones you need
If few years down the road and the whole jQuery UI become too bloated (say almost 300+ KB) to the point that it is heavier than your own content, I would call it far from being a standard. We're not sheeple folks, we don't need to put up with their boatload of bloat they're injecting in their jQuery components, especially if we don't use them. Let's be happy that we can selectively download (jquery-ui-1.8.12.custom.tab+accordion+datepicker+dialog+draggable+resizable.min.js) which ones we need on jQuery UI website; if there's no customized download facility on jQuery UI website, jQuery UI could receive flaks more than it deserves, and everybody will quickly find other jQuery components that is more lightweight than jQuery UI. Selectively choosing which jQuery UI you only need is the standard, downloading the whole package is silly.
jQuery Tools vs jQuery UI 14 KB(jQuery Tools) vs 209 KB(jQuery UI). jQuery Tools has the only most commonly used features a web program need, thus cutting down the bloat.
And the father(John Resig, see comment #5 of last link) of jQuery weigh in:
jQuery UI Tabs is only 6KB minified and gzipped, jQuery Tools Tabs is 1.5KB minified and gzipped – and that’s saying nothing of the features supported by both plugins.
See jQuery Tools in action
Download jQuery Tools. For future projects :-)