Freeview's terrestrial service supports high definition formats, so the PlayStation 3's tuner could be an HD unit. If so, it will be interesting to see whether Sony imposes any restrictions on high definition recording, and whether those recordings will be encrusted with DRM. It's possible that Sony could allow homebrew applications running under Linux on the PlayStation 3 to access the tuner, as well.
Of course, this isn't the first time Sony has dabbled in console-driven DVRs. The company's ill-fated PSX combined a PlayStation 2 core with a hard drive and TV tuner way back in 2003. However, the PSX didn't catch on and was only available in Japan. Thanks to Joystiq for the tip.