One of the biggest SEO issues on the site today is that the demos and docs pages have the same title tag "jQuery UI - Demos and Documentation" so these aren't descriptive enough and when they show up in Google's results, they look generic.
For each page, we need to have a detailed title that not only mentions the name of the plugin, but also loads in the keywords that a normal person would search for in Google.
For example, the title for Selectable should say something like:
"jQuery UI Selectable plugin - select elements by dragging a box or lasso with a mouse or using the control and shift keys for multiple, non-contiguous selections"
Ideally, these would be between 60-80 characters since Google only shows the first 60-ish before truncating in results but I think they parse the whole string so longer isn't terrible (within reason). Just make sure the first 60 characters have the most important keywords.
The intros for each plugin usually have good info and just need to be re-configured for the title to be tighter.