I love my Kindle Fire. All the gaming PDFs I've been amassing are much more useful and all those great books that seemed kind of pricey in hardback are now great as PDF options.
I've been using Dropbox on my various devices for a while now and it's a great way to make gaming stuff available on your computer, your phone, what have you. Strangely, Dropbox isn't available from the Amazon App Store yet.
If you Google for instructions on how to load Dropbox onto the Kindle Fire, you'll find many complicated ways to install it (via the USB port, etc.). Here are a couple simple ways to access your Dropbox account from the Fire:
1. Use QuickOffice (which is pre-loaded on the Fire) or QuickOffice Pro: You can associate your Dropbox account with either of these apps and, bam, instant acccess. QuickOffice Pro doesn't have its own PDF reader, so it will prompt you to choose one from those already on your device. This might actually be a plus over QuickOffice Pro if you don't care for QuickOffice Pro's PDF reader.
2. Use the Dropbox Android app: In order to do this, you first have to go to your Kindle Fire's "Settings" screen, select "Device," and then toggle "Allow Installation of Applications" to "On." Then, download the Dropbox Droid app right from the Dropbox website: link. Ta-da. You now have the Dropbox app on your Kindle Fire.
Alternatively, you could just use the SugarSync app. It is available from the Amazon App Store and seems to be more or less the same thing. I didn't use it because I didn't want to go through the hassle of switching from Dropbox.