This sort of language is routinely abused in a confusing manner. Usually when someone means "200% more/bigger/faster", they say "3x more/bigger/faster", instead of "3x as much/big/fast" like they should. At least in this case there's not really any ambiguity unless you think it's possible to spend negative energy.
3x more would definitely be interpreted as 4x the original value. If a product was advertised as three times faster when it was only three times as fast, there would be legal issues with false advertising.
At http://www.apple.com/mac-pro/performance/ , Apple advertises Thumderbolt 2 as 25x faster than FireWire 800. Thunderbolt 2 has bandwidth of 20 Gbps, which is 25 times FireWire 800's 800 Mbps.
