After installing CM9, with the 3.x kernel, on my Kindle Fire, I read about people connecting keyboards, mice and other USB devices to the Kindle Fire. In order to do this a USB cable referred to as a OTG cable is needed. I happened to order this one, but there were many options. After I got the cable, I plugged a USB 2.0 powered hub into the OTG cable which was then plugged into the Kindle Fire. A powered hub is essential as the Fire does not put out enough voltage to power most external devices. Also, on the Kindle Fire, you will want to install the applications "StickMount" and "File Expert" from the Google Play store.
Now for the big test. The first thing I did was plug in a USB mouse into the powered USB 2.0 hub. Much to my surprise a mouse cursor appeared on the screen and I was able to move the mouse around and click a few things. I was wondering if the mouse cursor would appear as the Kindle Fire is a touch screen device. Both the touch screen and the mouse worked at the same time, so nothing was lost. So far so good. I then plugged in my USB keyboard and then I opened a browser window and was able to type in the url on the physical keyboard. So now things are looking pretty promising. The next step was to plug in a USB flash drive. Within a second StickMount popped up a prompt asking me to allow it SuperUser access and then informing me that the USB device had been mounted in /sdcard/usbStorage/sda1. I then used File Expert to navigate to that directory and view the files on the flash drive. Everything seemed to be there and I was able to open and interact with files just like files found on the Kindle internal storage. Perhaps with the right USB flash drive, very low power requirements, the USB hub would not be needed and then you would have a solution to the limited space on the Fire. One of my sticks, a 4GB one, almost worked, but the 32GB one definitely would not.
Now for the things that didn't work. I tried to plug in my 1TB External USB harddrive and while the OS knew something was there, I do not believe the file system drivers were present. I also did not have much luck with my USB Bluetooth adapter. Also while these devices where plugged in I could not charge the Kindle Fire, so I was limited on how long the device would run. This adapter from Amazon may allow you to work around that issue.
So all in all the Fire with the OTG cable, a powered USB 2.0 hub, a USB keyboard and mouse can actually function as a basic computer. Now I would not recommend this setup for full time usage, but if you want something for some basic work that requires a lot of typing on the cheap, this would be one option. I also see no reason why this setup would not work with other Android devices. So if you decide to try this, I would appreciate some feedback.