Interesting find in the future schedules (but it's by no means set in stone as it's still a bit far out and Delta frequently changes their daily schedule). From March 2nd to April 9th, Delta will be operating one daily 757 flight between Boise and Salt Lake City. They put the 757 in the schedule from BOI-SLC for a single day on, IIRC, April 3rd, 2011. Next year it's on for over a month.
The 757 is the largest passenger airliner ever operated into Boise on a regular scheduled basis. The only time it's ever been operated as regular service:
2002 - North American Airlines (chartered by Hawaiian Vacations) one weekly flight to Maui
2011 - Delta's lone scheduled flight last year to SLC
2012 - Delta again, this time on a daily basis for a month.