Here's what Gmail Blog reports:-
Up until today, it's been a little tedious to send large or multiple attachments with an email. You had to select each attachment individually and you never knew how long it would be before those bigger files were ready to send.
Today, we're making some changes to the way Gmail attachments work. If you want to send a few files from the same folder, simply hold down the Ctrl key (Cmd on OS X) and click on each file you want to attach to your message. You can also hold down the Shift key to select a continuous list of files. A definite time saver.
You'll not only save a few mouse clicks selecting files, but you'll also see progress bars on each file as it uploads.