Chrome has supported multiselect for awhile, but the Windows versions of Chrome have had an annoying related bug. This is Issue 44068 in the Chromium bug tracker. Basically, the total length of selected files was limited to the MAX_PATH constant on Windows (256 characters). If the files you select had a total character count longer names than this, you would select the files but nothing would appear to happen.

This Chrome bug affected the SlickUpload 6 alpha (if you select too many files at once, SlickUpload will never get a selection signal, and won't be able to show the files or upload them). The Chrome 9 release fixes this bug by upping the number of characters to UNICODE_STRING_MAX_CHARS (32767 characters), so now you can select many files at once.

Happy multiselecting!