Actually jQuery runs about 80kb minified. But the actual filesize of the application doesn't always correlate to the speed of the application and the filesize of a javascript library is something we need not be concerned with since, like you said:
GameCharmer wrote:when you load a single page site, you don't have to reload the JS libraries.
As far as the should we host locally or on Google. Let me offer my 2 cents.
Security: Not really an issue in my opinion. It's jQuery...a javascript library used by everyone from huge corporations around the world to individual developers like you and me. Every release is beat to death with testing by many people. Even if something is wrong with a certain release, it's not like it wouldn't be tough to require an update to phpBB just to update jQuery. I'm sure by 4.0 you'll have an automatic updater like WordPress, right?
Parallel downloads: jQuery will load in parallel with other files regardless of whether or not it's on a different server. Try loading jQuery along with some other random JS files using <script src=""></script> while looking at the Net tab of FireBug. Servers can throw out more than one file at a time
Dependence: If you host something on Google, you are depending on another server for your content. The more you offload your files, the more at risk you are of having something broken - whereas if you host it locally with your installation of phpBB, the only time something would break is if your entire server went down.
Note: WordPress has jQuery hosted in wp-includes/js, not loading it off of some random Google server.
Speaking for AJAX:
AJAX is gonna be key for the survival of forums on the internet. I'm gonna be a bit harsh, but too many forum projects are kind of in the stone ages. Having an AJAX interface in 4.0 might spark a fresh interest in forums and keep the forum community alive. AJAX is extremely easy with jQuery, I hope to see some work done with it
