I want to create something to replace my television remote. I'm hoping to create a simple GUI that I can fiddle with on a touch screen. I'm not sure if this project is right for the Raspberry Pi or on the Android platform. Anyone have any experience with this?
I don't have experience with this, but if you look around online ("raspberry pi universal remote") you'll find a lot of people that do. There's even an entire site about it (or at least, a domain name with blog links).
The software side on the pi is LIRC. You also need to connect an infrared led transmitter (IR LED), which are less than a $1 US. I don't know what the range will be, but as lenik points out, the pi is not a mobile device and will have to sit in more or less one spot anyway. As per that "Open Source Universal Remote" site linked above, presuming you have a wifi LAN, the best idea is probably to have the pi run a web interface that you can then access on, e.g., an android phone.
If you are looking for a DIY learning project, yes, the Raspberry Pi can be used to build a TV remote. You can find small TFT touchscreens, cases, and IR blasters easily via search. It won't be the most practical remote, as mentioned in the comments, because of its size and power requirements, but it might be OK as a tabletop remote where you can keep it plugged in.
Some TVs can be controlled via TCP/IP, avoiding the need for the IR blaster, but you're going to find it harder to find the details of the protocol for some TVs.
For Android, some devices are available with IR Blasters. HTC, LG, Samsung have all offered models with IR support; each manufacturer has their own TV remote app (may not offer universal support). If you want to learn Android development, you may want to check some of the Android-tagged questions on stackoverflow.com
It is a feasible project for the pi, but not for the android platform. If you want to use android, get a mobile phone with IR transmitter and a corresponding app and you're done. But its kind of boring then. Interfacing with an IR transmitter directly on android will be much more complicated than when using a normal linux distribution and a nice library for your IR hardware.
For the pi you should get raspbian (or any other standard linux distribution) on it, an IR transmitter and possible a sensor (so you can record signals from the original remote control) and the touchscreen.
If your IR transmitter is high level like an usb device you probably can use LIRC to interface with it, but it may be more interesting to use a (much cheaper) low level transmitter/sender and program it directly. You should be able to find easy howtos on different pi instructable sites, often with a ready made python module to control the GPIO pins.
For the GUI you can either use some X11 toolkit or some nice graphics library for the framebuffer drawing a fancy interface yourself.