The right PIC for the job can make many projects seem trivial. The 16F917 is perfect for a thermostat with display. Its packed with many great features; LCD controller built in, 10bit A/D, USART, Nanowatt tech, low power oscillator, low vdd detect.
I considered seven segment LED displays in the original design but on a small PCB the heat (even the 4ma HE displays) was picked up by the temperature sensor (about 2c)
Even the mighty 16F917 has a couple of quibbles though such as no MSSP & USART at the same time (they share I/O pins). But I'm not using the MSSP (almost did though)
Another really nice featue I've yet to play with is the low vdd detect mode. Should be handy as a on battery indicator (sleep & save power but keep the clock updating)