The new SI units

"Have you heard? The smiths won the lottery last week and the house they're looking to buy has a garden the size of 2 football pitches!"

But a football pitch can vary in size from 4,050m² to 10,800m².

And new mp3 players are often quoted as being able to store a certain number of songs, for example the 1Gb iPod shuffle can store 240.

But is this 240 average 3½ minute radio edits?

Or 240 20-minute drum and bass epics?

Or does it even matter?

Using a commonly known "thing" means far more to the average user than an exact figure. Approximating information is a good thing.

If you're only presenting information with 1 or maybe 2 significant figures, do you really care how accurate the unit is?