I moved out to Perth 4 months ago and this is just what I have found so far:
Pro's:
Great beaches
Great climate so you can actually plan days out etc
Good laid back lifestyle (see con's also).
Some beautiful places to see and spend free days out, e.g. Kings Park is amazing!
If you have a good work ethic, the career prospects are very good here.
Perth is a place that is growing and developing and a lot of money is being invested into the CBD.
The CBD is small (not really like a city), but clean and attractive and not over populated.
Free BBQ's everywhere is great.
Most workplaces are generally supportive of a work/life balance.
There is a sense of optimism in the City unlike the negativity you find in the UK.
Con's:
The landscape is dry and barren and acres of bushland is split up by newly built concrete housing estates.
Shopping is terrible in Perth! You will get sick of the sight of Target, KMart, Woolworths, Big W, and Coles. The only place you can buy anything sesembling nice is Myers and David Jones
It is backwards, customer service is shocking and it will take you years to get anything done. Locals just don't seem to have any urgency about anything or even care for that matter.
It is full of Brits. (Now please don't take offense because I am british myself, but I didn't come to Australia to live in little britain).
Local people from Perth are very clicky.
It is rough (unless you are loaded and can live in a very affluent area) and full of Chavs and Bogans.
The whole place is dead after 7pm (shops close at 5pm) and there is generally nothing to do in the evenings.
FLIES!!!!!!
People think that driving in a clapped out 4x4 gives them status and people love to drive up your a*se on the roads.
The cost of living is expensive compared to the UK, however, the wages are much better so it is relative.
You need a car to do anything as the public transport is pants!
The rental/housing market is ridiculous and overpriced.
Look, as most people have already said, these are just opinions. Like anywhere I have ever lived, there is good and bad. I think the problem is when people start dreaming of the promised land that they are moving to and the realityies of life hit them when it doesn't live up to billing. It completely depends on what you are looking for in life. Some people love it, some hate it. Personally, I have enjoyed the last 4 months. The comments above are merely observations I have made so far so I hope people don't get offended by it.
My advice would be to come and see it for yourslef and don't commit long term until you know it is where you want to stay. I hope it helps.