As a future (in 2 weeks) Imperial student I'm proud, but at this point, does anyone really still care much about the tables?
The weights for various metrics are arbitrarily chosen, and choosing one set of weights over another will change the rankings significantly (at least with the top few). You can choose the weights to make the ranking say more or less anything you want (within reason).
I would only use it as a very very rough guide. Anything in the top 10 are probably about as good.