Should I buy one now or wait to Haswell?
It's not like they are going to increase the price once their models with Haswell appears and once they bump the specs it (speaking of the rMBP 15") will probably get better dedicated graphics too so either you buy it now or wait until then and get an even better laptop. Because now, the only thing they did was a small increase in processor speed and lowering the prices for both the laptop and upgrading the specs (like upgrading SSD etc) and these prices won't increase so practically it comes down to this:
You buy it now since you need it now or
You wait and buy an even better laptop once Haswell is released, if time isn't running out.