Adding SWFUpload generates more dependencies: You need both Javascript and Flash available and enabled on the client (installing NoScript usually disables both, and Flash is not available for all platforms), and you need CSS available and enabled on the client unless you really want to confuse the user. And unless you want to really nag and confuse your user, you need a working fallback strategy using classic HTML forms and file upload fields. So, you also have to make your server side code more complex.

I've discussed this over and over again, and unless you have a VERY controlled environment where users have to use a selected client program with a configuration that the users cannot change, tools like SWFUpload that require Javascript and plugins but do not offering working fallback code just do not work. Stick to plain HTML and use Javascript only to enhance existing features and there will be no such problems.

Alexander