Spotted this tweet just now:
tonybibbs: Downloads from jqueryui.com are invalid ZIP files...in case anybody has a jquery contact.
I tried to replicate the problem and on Win XP and on a Mac it will not open and says that the zip file is corrupt.
To replicate I went to the download page on jqueryui.com and left all the options as is and clicked the download button. I set it to open and it presented a message that the file was invalid or corrupt.
If you leave all options checked you get the invalid and corrupt message.
If you uncheck Effect "shake" you get a working zip file.
If you only download Effect "shake" with whatever dependencies it determines you need it also works. Not sure what's going on but hopefully this helps.
I just tried to download the 1.5.3 release and it downloads fine so the problem lies with 1.7
This is for the Download button on the right column not the quick download.