Apparently it weighs quite a bit?
This was quite an intriguing bit of info for a throwaway line like that. How did it go? 'the TARDIS's weight is always adjusted; if it were not, its weight would shatter the Earth's surface.'
The TARDIS is kind of amazing in any number of ways but i'm amused at the insight into Time Lord mentality... here we have an obsolete ship that can seemingly destroy the Universe with minimal effort and can crack a planet in half just by 'relaxing'.
Just the thought of building the damn thing in the first place should give any sane person serious thought. Like General Motors suddenly started making cars with nuclear reactors for engines...
Sure, the mileage is amazing, but when you crash one of the buggers?
Also, it kind of makes you wonder what a dedicated War TARDIS would be like.