Yahoo's YSlow tool recommends that these files are combined and minified, and Tapestry includes functionality to do the first (minifying is on the TODO list I believe) probably as a response to this recommendation which is good. Unfortunately the implementation based on only having the JS files required for a page means that the combined JS can easily be unique for most pages of a site. This means that the client browser has to download & cache lots of large JS multiple times (prototype, scriptaculous, tapestry etc) as part of bigger combined files, which I think is probably worse than requesting them separately, but only downloading stuff once and using that for all pages.
To solve this issue, Tapestry script combination could combine all of the scripts needed for the site, and not just the unique set for each page. That way only a single JS file needs to be downloaded and cached by the client browser. I'm aware that this may not be that easy given the existing way only scripts needed for the page are put on it, so an alternative solution that may be easier to implement would be to combine scripts into two files for each page. The first file would contain all of the commonly Tapestry provided JS such as prototype.js, scriptaculous.js, effects.js, tapestry.js, etc in one file that's the same for every page, and have the rest in a second file that is unique for the page but that is not likely to include very large JS files, just many little ones.
A second flaw that the combination has is that if an external JS file is requested, script combination is aborted rather than just excluding the external file from the combination.
One other thing that surprised me about Tapestry's script combination is the length of the generated filename, for example it's 919 characters long for a page on our site.