Loyalty vs. Opportunity

So about a month ago my boss told me I should probably start looking for other jobs because the only grant funding we had left was due to expire this coming Sunday. I went home and sent out a flurry of graceful applications to as many jobs as I could find posted in the area. Since then the lab has been rescued by an ARRA-funded challenge grant. Now, though, I'm beginning to hear back from the positions I applied to.

The new grant in my current lab presents me with new opportunities to expand upon techniques I've already learned and finally generate some real data. But at the same time, these other positions potentially represent very real opportunities to sink my teeth into an entirely new system and expand my skill set. My current position is applied immunology/microbiology, the potential positions are more basic immunology.

I find myself caught between loyalty to my current boss--who has taught me quite a lot but at the same time also left me alone in the lab and expected me to move mountains with chopsticks (and no glue to make a bigger lever)--and feeling that moving into another lab with another PI and even broader immunological focus would make my application to graduate school this fall stronger. However, this premise itself could be false. I know that in looking for a job, it's a major black mark to have drifted among several labs for short periods of times; but is the same true for graduate schools? I've spent 2 years in the current lab, if you combine the time I have spent here as an undergraduate student, temp, and staff. Would the grad school admission committee see my moving into another lab shortly before applying as a negative quality?

I'm tempted to send out the information requested and attend any interviews I am offered. If they wish to follow up my references, of which my boss is one, I will let her know that she may be getting some calls. Yet I worry that doing so will endanger a good recommendation letter from her.

Therefore I find myself at somewhat of an impasse.

UPDATE: I went ahead and sent out the requested information and affirmed my interest in the position. It's not even an interview yet, so maybe I'm making chromosomes out of oligomers. But still, it's a research assistantship instead of tech position, so I feel it is wisest to pursue it and see what may come of it.