If you can – don't use jQuery. There several advantages to it.
First of all people wouldn't need to download that much garbage, which won't be used anyway (you use only some jQuery functions, right?). Prefer using libraries suited for your specific needs – these in most cases are lighter (about 80%) and faster...
Secondly, all that garbage wouldn't be executed – that too drains several microseconds of CPU time.
Thirdly, hand optimized plain JavaScript itself executes faster.
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Here's an interesting back-of-an-envelope calculation
http://forum.jquery.com/topic/make-a-light-version-of-jquery-jquery-lite#14737000002712094
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If you can – don't use jQuery. There several advantages to it. First of all people wouldn't need to download that much garbage, which won't be used anyway (you use only some jQuery functions, right?). Prefer using libraries suited for your specific needs – these in most cases are lighter (about 80%) and faster... Secondly, all that garbage wouldn't be executed – that too drains several microseconds of CPU time. Thirdly, hand optimized plain JavaScript itself executes faster.