I would like to bring your attention to google docs www.docs.google.com
its a web 2.0 workspace where you can upload PDFs and also create, edit and upload text files (.txt, word, open office, HTML, RTF) spreadsheets(excel etc) and presenations (power point etc) and its 100% free
I have been using it to store my PDFs as soon as I have downloaded them from journals, which is really useful due to their acessibility and the fact that i wont lose them due to hard drive/memory stick failure or neglenece on my own behalf...
I also use it to store my spreadsheet data, graphs and research presentations which again is really useful as i can acesses then anywhere with an internet connection and I wont lose them due to hard drive/memory stick failure or neglenece on my own behalf...
Furthermore you can share documents with people you choose to, so you can immediately share your results with your fellow group memebers and collaborators. However! you can't share copyrighted material (so I think the sharing of paid 4 papers is not allowed unfortunately) there are aslo a few more googledoc rules you must abide by or risk being banned.
Now I think googledocs is absolutely faboulous, however it does have some restrctions past the above mentioned copyright enforcement. You have to have a googlemail address (but as with docs this is free) the main restriction is the size limits imposed by google, in particular the limit of a 100 PDFs, but you could always raise this to 200 if you opened another account, prehaps 1 account per paper you write would be a good idea as you could store all your results, references and maunscript all in one highly acessible place forever...You can find details of size limits by clicking here
however I think you'll find that the limits of other file types are not so bad 4 us scientists. so have a look get a googlemail
account and join up to googledocs