If you're not already using it, or some other form of javascript library you are already so far behind the eight ball in regards to professional javascript web development it's almost laughable.
You're utterly insane if you don't add a javascript framework to your web development repetoire. jQuery is one of the most popular because it's also one of the best and simplest to start with - it will be around for a very, very long time.
End original answer
Addendum
Ok, so after re-reading my answer I can certainly see how people could see it as rude and for that I apologise - I'm leaving the original answer so people have context. The indication I got from the original question was that the submitter hasn't chosen a framework at all for development and frankly I was fairly shocked that in this day and age people are still trying to hand write the kind of javascript UI interactions clients expect in web development.
Some reasons you need to choose a framework:
- You're killing yourself and your development time if you don't.
- You get to concentrate on the fun bits of development and ignore the incredibly boring compatability bits.
- Ajax is easier
You can get a fairly detailed comparison of various frameworks here.
Some reasons you should choose jQuery:
- It's a piece of piss to learn
- Very active author
- Good test structure - they test one version ahead (where available) and one behind on all major browsers as well as the current version
- A robust plugin society
- An intriguing new test environment for javascript
Here's the best bit - even if you started learning jQuery tomorrow and it stopped being useful three weeks from now it still wouldn't be wasted knowledge because it's just a framework. By using it you're still getting better at javascript and no mater what happens to any of the frameworks HTML5 and it's new API based elements guarantee javascript is going to be around for a very time.
On a slight tangent regarding my original answer, I thought it was a little amusing that the first person to complain I was being rude was from Switzerland. I don't think I've ever met a rude Swiss person. Then the next person who commented with a 'What rudeness?' was from New York. Heh - I probably couldn't be rude enough to register with a New Yorker if I spent hours trying to craft the rudest response I could muster (it's not that NY's are particularly rude, I just don't think they notice it when others are).
Somewhere in between those two extremes probably lies everyone else; so for those people who did think I was rude, I apologise and hope this expanded answer helps clarify my original thinking.