Well, after having worked with jQuery now for a good few months, i like to think I've got a good understanding of what it can and can't do. Now, let's get onto the more interesting negative aspects.
There are some features which are missing, such as how do you get the selected index of a select (combo) box? Using the val() function, you can easily get the value of what has been selected, but there doesn't seem to be any function for the selected index.
It can be slow. Yes I know I'm going to annoy some people with this comment, but sometimes it takes quite a few seconds for a function to complete. Mostly, it's very quick, but when there are a lot of elements on a page with the same class, and I want to get them into a single object and perform a function on them, it's often faster to hide a count in the page, number the id and use a for loop instead, than to use $(".nameOfClass").each(function() { ... }). Also, the click() and other event binding functions are slow for the same reason. It's much quicker to write the onclick function into returned html from an ajax query than it is the use the click() function to assign the click to an event. There are a few other minor niggles, where i have to resort back to using the standard DOM accessing methods.
Now the positive, it can do pretty much everything you could want. It's what javascript and the DOM should be, that is, each element (or group of elements) should be easily accessible and editable. The time it has saved me is great, and what i am now able to create is beyond what i could have expected from javascript. The scope of plugin development seems limitless, and although there are only a small number of plugins, many of the are invaluable (although somewhat delicate, such as the Date Picker, which i've only managed to get to work properly in 1 in 3 projects).
Overall, i'm going to stick with jQuery, and hopefully they'll develop it further and add the missing functionality. Although more than likely i'm just missing something...
Merry Christmas everyone, and have a Happy New Year!