Interesting point about tax issues, @dfrazer, I never thought about that particular aspect…
I use Dropbox as well, for delivering design projects as well as photos. It works very well for that purpose, since I can just copy the file(s) to a folder on my computer and they automatically upload in the background.
I realise that becomes unpractical if there is any amount of back-and-forth between you and the client. In that case you need a service with client proofing.
I confess I don’t quite understand what you’re saying here. 🙂 Especially with design projects I often go through several iterations before the client is happy. I usually upload the updated file and send a different link, although you could just overwrite the original file and use the same link if you wanted to.