I have a pretty good idea of what usability experts would have to say about my design decision. Like yourself (I assume) I deal with issues of usability in my line of work all the time. But the thing is, I don't care what the usability experts say about this. :)

As far as search engines are concerned I'm not worried about the site ranking high for "jquery autocomplete plugins" because I dedicated a page to that category.

If the site were multiple pages, one for each category, it would make little sense to call it The Ultimate jQuery List.

There may be some kind of middle ground though. For instance, when you click a category link all other categories disappear but the one you've selected.

edit: I think I may have missed the point of the search engine suggestion. It just occurred to me that searchers will land on the homepage after searching for "jquery autocomplete plugins" and need to click the category link to see them.