Well I'm very new to all of this so I may find out differently down the road, but personally I have had no problems with 2.0 Ohm 306 attys on my 650 Mah eGo batteries. After a few days of trying 510 attys, regular cartomizers, lr cartomizers, and dual coil cartomizers I have settled for the moment on using the 2.0 LR 306 with an extended drip tip to cool the vapor a bit more than the short tips. I have been using two atomizers for alternating tobacco and fruity flavors over the last couple of weeks.
I can understand the part about shorter battery life as the current draw is higher with a 2.0 Ohm atomizer over a 3.0 Ohm atomizer. Assuming your eGo is putting out 3.4 volts (which mine is) then the following would be true:
3.0 Ohm atomizer would draw 1.13 amps of current with power of 3.85 watts
2.0 Ohm atomizer would draw 1.7 amps of current with power of 5.78 watts
So battery recharge cycles are going to have to be more frequent and perhaps the increased load and heat will shorten the overall life of the battery. Either way, I don't mind the charging and thus far have had no issues. I also think this is likely elated to screwing the atomizer onto the battery too tightly. Just seems like the most likely case.
You can run your own calculations here if you wish:
Ohm's Law Calculators
Hope that helps in some way.