Since installing Ubuntu 12.10 I have been playing around trying to get my Radeon HD 5450 gpu to work with the proprietary driver, as from the start installing the driver meant losing unity.

I won't list the steps I took as it is not a requirement to answering this question.

After taking one measure and then installing fglrx-updates, upon reboot the system hung at the purple screen. So I decided to boot using nomodeset

I edited

quiet splash $vt_handoff

to look like this

quiet splash nomodeset

Making this change I am then able to log in with Unity and the proprietary driver installed and performing well. I would go as far as to say it performs better than it did in 12.04

fglrxinfo reads

display: :0  screen: 0

OpenGL vendor string: Advanced Micro Devices, Inc.

OpenGL renderer string: ATI Mobility Radeon HD 5000 Series

OpenGL version string: 4.2.11903 Compatibility Profile Context

Please note the way I have added nomodeset It had been a while since I have had to do this so it was done from memory.
When looking for an answer to this question I came across this and discovered that my edit was supposed to go from

quiet splash $vt_handoff

to

nomodeset $vt_handoff

What has my nomodeset edit done? The only thing wrong that I have noticed is that I don't get the plymouth Ubuntu logo screen when booting.

If that is the only trade-off I am happy to make the edit permanant.