I've also been using Zotero for some time now to manage my references. What's nice about Zotero over RefMan, EndNote and others, is that it runs inside Firefox, and when you're on a Pubmed or Journal website, you can save a reference and the PDF with a single click within your Zotero library. Zotero also interfaces with both MS Word and OO.o, and uses all the standard EndNote styles for formatting bibliographies.
You can also sync your Zotero library, including all your references, snapshots of the HTML version of all your articles, and all the PDFs using the Zotero servers. This syncs your library to every other computer you're using. This is nice when you're away from the office and need to look at a paper, but you're not on your institution's LAN and journal articles are paywalled. The problem with Zotero is a low storage limit - you only get tiny 100MB storage space for free. Have any more papers or references you want to sync and you have to pay for it.
That's if you use Zotero's servers. You can also sync your library using your own WebDAV server. Go into Zotero's preferences and you'll see this under the sync pane.
Here's where Dropbox comes in handy. You get 2GB for free when you sign up for Dropbox, and you can add tons more space by referring others, filling out surveys, viewing the help pages, etc. I've bumped my free account up to 19GB. Dropbox doesn't support WebDAV by itself, but a 3rd party service, DropDAV, allows you to do this. Just give DropDAV your Dropbox credentials, and you now have your own WebDAV server at https://dav.dropdav.com. Now simply point Zotero to sync with your own DropDAV server rather than Zotero's servers, and you can sync gigabytes of references and PDFs using your Dropbox.
Why not simply move the location of your Zotero library to a folder in your dropbox and forget syncing altogether? I did that for a while, but as long as Firefox is open, Zotero holds your library files open, which means they're not syncing properly. If you have instances of Firefox open on more than one machine you're going to run into trouble. Syncing to Dropbox with DropDAV only touches your Dropbox during a Zotero sync operation.
What you'll need:
1. Dropbox. Sign up for a free 2GB Dropbox account. If you use this special referral link, you'll get an extra 250MB for free. Create a folder in your Dropbox called "zotero."
2. DropDAV. Log in here with your Dropbox credentials and you'll have DropDAV up and running.
3. Firefox + Zotero. First, start using Firefox if you haven't already, then install the Zotero extension.
4. Connect Zotero to DropDAV. Go into Zotero's preferences, sync panel. See the screenshot above to set your Zotero library to sync to your Dropbox via WebDAV using DropDAV.
You're done! Now, go out and start saving/syncing gigabytes of papers!