Do you have something now that you can use?
If you wait, it will probably be 2 months, if not 3 or 4 for a wide choice, and even then prices might not be cheap, so it depends on what you want to spend.
The best part about Haswell will probably be battery life, so it depends on what you plan to do with a laptop, and whether you need a long battery life.
Non Haswell machines might also drop to try and clear stock.
I bought a Windows 8 tablet last year to play with, and had the idea to upgrade to a Haswell tablet when they came out a year later, but given how much/how I use my current tablet, I'm not sure there's any real benefit Haswell would bring and I probably won't bother now.
It's all about what you need from a laptop and when you need it.