I can't immediately think of any really big differences, and the ones that do exist are more down to cultural differences (e.g. Google has a much more involved/

I can't immediately think of any really big differences, and the ones that do exist are more down to cultural differences (e.g. Google has a much more involved/rigorous code review process, which is reflected in their tools). Mercurial is definitely better than Perforce/Piper, but IIRC Google now actually has a very similar mercurial frontend wrapper that a lot of employees use.