I noticed this issue with both Safari and Webkit when testing a 32 MB Flash swf file and it was re-downloading from the server every time I loaded the page regardless. With the same file Firefox and Internet Explorer loaded immediately from cache on the second loads. I don't know if it's a Safari issue or a webkit issue, but files larger than around 9 MB are not being cached. I initially tested with swf files thinking it was a flash caching issue, but later added png and jpg files to my test and they both act about the same. If you visit the link about and click the test4 files they should load and then re-load from cache as expected on 2nd visit. I recommend Command-clicking the links to open them up in their own tab. Close the tab, and Command-Click again to test the cache since re-loading the page can sometimes trigger a re-download anyway. When you click on the slightly larger test3 files and click the same as above, they re-download from the server every time. To caching larger files is the more necessary function since they're the ones you have to wait longer for. Note that the samples only consist of images of noise, so they shouldn't look like anything when loaded.
A resource of this type would be handled by the CFNetwork cache, which is not part of WebKit. You should file a bug report about this at <http://bugreporter.apple.com/>.
Ok, I filed a bug with bugreporter. Let's see if anything happens. I suspect if it's only an issue with 10.5, then I'm probably out of luck.
Thanks. Can you please post the bug ID here for future reference? I'll close this bug since this is not a WebKit issue.
Bug Reporter Problem ID: 7214260 Were you able to confirm the issue on your end? What hardware/OS? Mine is PPC / 10.5.8