In reply to Daniel Duerden:
I've not read all the above responses Dan, but my opinion for what it's worth is this. Your decision is based on two things really - one is the stability of your relationship, and the second the housing market.
If, and only if you are absolutely certain that your relationship will continue to work well when you live together should you consider buying together. I do not say this to put a question over it but living together for the first time does put a lot of strain on a relationship, and you will learn a lot more you didn't know about one another! Most of the time this will be all for the better, but it can go the other way too. You shouldn't see this as questioning your relationship, but more considering whether you are ready for taking two big steps together.
Re the housing market, the decision to rent or buy is dependant upon your ability to pay the mortgage in the long term and the way the housing market is likely to go. If you have a stable and guaranteed income (i.e. should your firm make you redundant, how quickly could you find a role of similar standing/remuneration), and have the flexibility to cope with rises in interest rates beyond the current level then you are in a good position to buy. You must consider longer than the fixed term of any mortgage though - the market may be in a worse position when it ends so your payments could rise significantly at that point, question whether you could cope with a 2.5% increase in interest rate for example.
If you are not in this position then you are more at the mercy of the market. My own view is that the bottom end of market is likely to fall out some time in the next 12-18 months, with lenders calling in debts from defaulters - i.e. repossession. This will result in lower house prices in the lower end of the market, but should you have the ability to pay your mortgage through this you will not be affected - until you come to sell.
It's a complex situation and can't be answered with a simple 'buy' or 'rent'. Consider your position fully before diving in, it is anybody's guess how the market will change.