Well, it's not polished yet, but preliminary tests show that the Raspi has enough power to do some simple NFM software-defined radio work with RTL2832U-based DVB-T USB TV tuners
I was able to compile rtl_fm
(an optimized version of Osmocom's rtl-sdr
software), which allowed the Raspi to tune a frequency (162.55 MHz, weather radio band in the US) and play it real-time. The Raspi's internal sound kept hanging, so a cheap USB audio device was used instead. The audio is choppy, but CPU usage is only around 62% - which is promising.