It is difficult to be accurate without using a stopwatch, but with our HD TV, 3.8Gb is about two hours television. Wonderful. About.
I will time it accurately when I am prepared to watch Glee all the way through. It still has a tea-break for some unknown period before it starts recording again.

The STB is indeed recording 3.891Gb segments, according to the computer.
So, the STB is never going to record an evening's TV without irritating breaks whilst we are out for the evening, nor a televised film of any length.

Sky is the obvious way for us to go, or another STB which is WAY upmarket of this one. Makes you want to spit.