I wonder how the EMB-170,175,190,195 models are faring? Last I heard they're supposed to be pretty good.

Regarding fuel efficiency, I think whenever planes will get the new P&W geared turbofans they'll win the cake. Although, the defining factor among that group is which plane has the slickest airframe.
Pratt & Whitney: Commercial Engines - PurePower PW1000G

For airlines better fuel efficiency means nothing though unless other operating costs and investment costs stay the same or reduce as well.

Not to be snotty, but define "regional"

Pure jet engines are significantly more fuel thirsty than turboprops for a given distance travelled. Turboprops are generally much slower than jet aircraft. Is efficiency as it is used in this thread a specific fuel consumption question or a time is money question?

I would think that if fuel goes up and stabilizes in the $150/barrel range, you will see lots of unducted fan (turboprop) aircraft on the drawing board.

They burn more fuel per seat than their similar-sized CRJ competition.

But they can also carry a heavier payload. But I guess it would not matter if it's operated on a fee for departure basis

I heard a story today from a somewhat reliable source that some carriers have expressed an interest to Embraer to start making the Brasilias again. Supposedly they (Embraer) are investigating this. I think now that the problems with the earlier versions have been addressed it could be a viable, efficiant short/medium haul option. Sure be interesting to see if anything comes of this..:D