WeaverBox now supports both Flash and HTML5 uploads for files. Although both methods do the same job (upload files from a users computer to the server) they work in slightly different ways.
Flash upload supports file chunking. This means that a large file will be cut into many pieces and uploaded, bit at a time. This process enables you to bypass the normal 12MB file size limit most web hosts impose. Once all the 'bits' have been uploaded, they are joined back together again to form one, single complete file. However Flash is not supported on devices like the iPhone and iPad. Also a growing number of people are opting to disable Flash in their web browser, to limit crashes, conserve battery power, save bandwidth and to hide adverts.
Ultimately the type of upload mechanism you decide to implement depends on the type of website you are building for. For a smaller corporate website where the bulk of users are browsing using Safari, Firefox or Chrome, you could probably use the HTML5 upload. But for a more public-facing website, the default Flash option would probably be best used.
Of interest, if a user does have Flash disabled on their computer and is unable to upload files, Google Chrome can be used instead. This is because Google Chrome includes its own Flash plugin, which runs separately to any Flash plugin the user has previously disabled or deleted on their computer. So for people having difficulty uploading files to your DropBox, you may wish to advise they try Google Chrome instead (which is a free download).