Has it been done? Yes. Is it safe? That's relative. More boost means less room for error. If you run the smaller pulley and in a turn or hard acceleration cause cavitation in the fuel pump there's a greater chance of damage. It's a risk/reward question really. If you're going to do it you'll definitely want some sort of tuning capabilities (maf cal, UCON, etc.) to fill in the wholes in the TRD tune (if that's what you're currently running).
I've got full exhaust, intake, and 2.825 supergrip pulley. I've got a maf cal, which has yet to be tuned. I'm waiting until the truck in no longer my daily driver before I think about upping the boost.
@Hard Taco on the other hand, is running the 2.7 with a maf cal. It's all about the tune.