Alright so here's the current pricing in my area:http://bitcoincharts.com/charts/
$120 for a 5770
$260 for a 5870
Should I jump into this mining boat headfirst and buy a 5870? Or is the difficulty increasing so fast it won't be worth it to recoup my investment?
seems to indicate it'd go down next change.
Your purchase should depend on the price of the rest of your rig, PSU wattage, likelihood of buying a new rig/new parts and acceptable noise/heat generation levels taken into account.
Recouping your investment isn't assured, but you will offset the devaluation of your hardware over time.