It seems a little less stable than version 9 on Linux, at least 64-bit (it’s kind of complicated, because they only have a 32-bit program, so you either need to run a 32-bit version of your web browser, or use a wrapper that will let the 64-bit browser talk to the 32-bit plugin. nspluginwrapper does this for Firefox and other Gecko browsers, while Opera has a wrapper built in). But the annoying part: WordPress’ image upload no longer works.
Current versions of WordPress use SWFUpload to provide an enhanced file uploader. If you don’t have Flash installed, it will just use the standard upload dialog built into your web browser, but then you’re stuck uploading one image at a time — a real pain if you’re making a photo gallery post. Unfortunately for upload libraries, Adobe removed the ability for the Flash API to open a file dialog for security reasons.
So now, you can click on the button, but the dialog never opens. WordPress is tracking the issue in ticket 6979, which mentions that SWFUpload is discussing workarounds, and the YUI Uploader has already released a new version that works with Flash 10.
An update of some sort is likely to happen soon. In the mean time, WordPress users have two choices: hold off on updating Flash, or stick with the browser uploader for now.
Update October 31: SWFUpload has a new version in beta which works with Flash 10, and WordPress is working on integrating the update. It’s targeted for WordPress 2.7, which comes out in a little under two weeks, though the 2.7 writeup lists it as a feature that “didn’t make it” and might be in 2.8. (This seems like something that would affect enough people that I’d hope they would include it, even if it means pushing back the release a few days for more testing.)
There’s also been talk about implementing a file uploader using Gears, which I’d find really appealing if I weren’t 64-bit Linux both at home and at work.
Update November 1: I’ve tested WordPress 2.7 Beta 1 (not on this blog) and can confirm that the fix is included, as I was able to upload two images in one transaction.