Thanks for the answers.
What I want to do is similar to a remote keyboard, I don't want to mix USB with BT , what I meant is that having an USB interface while you are prototyping looks like more flexible, to program the chip etc, the final version wouldn't need USB.
As for the power issue I was searching a little and saw this:
In the Atmega328 datasheet:
Power Consumption at 1MHz, 1.8V, 25°C
– Active Mode: 0.2mA
– Power-down Mode: 0.1?A
– Power-save Mode: 0.75?A (Including 32kHz RTC) (0.00075mA)
And from Energizer cr2032 datasheet (3V 250mAh Li Ion button cell battery) :
with a load of 68,000 Ohm, drains 0.043 mA for 721h (30 days) at ~3V
If at the 3V of the cell (roughly double of 1.8v) and more than 1Mhz the chip drains 0.4mA in active mode instead of 0.2 it looks like it would
discharge about 10 times faster or in 72h since 0.4mA is 10 times more than 0.043mA (the sample load from energizer) very roughly
But my application only needs non continuous transmission so the chip would be in power save or power down mode most of the time.
I saw this guy disabling many things inside the chip and getting it to "work" with as little as 1 micro ampere and a coin cell:
http://www.sparkfun.com/tutorials/309
of course for my application there is also the bluetooth chips.. I was searching information about this JY-MCU one but I don't
see which IC's it uses or any info about power consumption, anyway, powering the atmega + bt with just a coin cell doesn't
look very doable.. 
thanks.