I'm running way ahead of myself being an arduino noobie but I was thinking of consolidating the knowledge I'm picking up as I go along and testing myself on something practical once I've reached a certain milestone. One thing I had in mind is to see if I can produce a cat logger. Let me explain.
Our cats have microchips which are used in proximity to the cat flap to let the little buggers in and out. I was wondering if it is possible to get something, do something, which would let me record the chip number and the date and time the little feline swines go in and out? Clearly there are chip readers out there but is it possible to do something like I have in mind on the uno/leonardo boards? I've no problem if there isn't but I thought it would be a useful project to try and do once I get to a point where I can do a bit more than light an led or two.
EDIT: A quick bit of research suggests the chips are RFID chips but there seems to be some ambiguity whether the frequencies are national standards or if different types apply.
arduino_obc_and_rbc:
little feline swines
Haha! 
Yes that is absolutely possible assuming you can interface to the existing system that controls the door or install an independent sensor to detect the swine chips. Probably would want a real-time clock and somewhere to log the data to. This could be an SD flash memory card, a web site, Twitter, etc. How about a notification to your phone every time? 
Jack, I spent a little more time looking into it and there are definitely some folk who have asked similar questions elsewhere. It does seem you can buy off-the-shelf readers to read the chip so I guess once you've got that information then writing the data somewhere will be a doddle.
The idea of using twitter has a certain appeal. I look forward to the day when Google bring out a KittyCam. I can't see a cat wanting to wear it on its head but I can think of somewhere where it could go.
There was another Thread recently in which someone wanted to identify wagons on a model railway. Someone suggested using animal RFID tags and an RFID reader. That leads me to think you could read the cat chips with a separate reader connected to the Arduino. However I have never experimented with RFID.
...R
Robin2:
There was another Thread recently in which someone wanted to identify wagons on a model railway.
That was me. I've not done anything about it yet.
I was intrigued by the subject of this thread, as I initially thought it referred to some exotic foreign food substance. 
Someone suggested using animal RFID tags and an RFID reader. That leads me to think you could read the cat chips with a separate reader connected to the Arduino. However I have never experimented with RFID.
Neither have I, but I'm assured it does work. What I couldn't find out was (for my own use, whether the pet tags could be reprogrammed, and) what is the frequency the pet tags work at. There are 3 types of RFID devices, standard, VHF and UHF. As the tags are very small, about the size of a grain of rice, I suspect they use UHF.