If you assume the goal of all this is to deter future leaks, I'd say they are doing a pretty good job. Snowden has so much uncertainty and risk in the next few weeks that I bet borderline whistle-blowers are rethinking their plan.

Arresting him quietly without the media gets them Snowden, but not the deterrent.

In both cases they seem to be overplaying their hand. Dotcom has a very real chance of getting off largely because the way it was handled have included such blatant disregard for the law. E.g. without the revelations of illegal spying, and the massive overkill of the way his arrest was handled, it might have been a lot easier to gentle "suggest" things to a judge and make the whole thing go away. Instead they've ensured that it's really hard for the judges involved to not treat this seriously.

Same with Snowden - creating a diplomatic incident that now has pretty much every Latin American leader screaming bloody murder and have officials describing it as virtually a kidnapping, and complaining about colonialism, means European countries and others will quickly start seeing that there's a very high potential price to pay for bending to US demands in this, in a case where they likely have little sympathy to the US position in the first place given that pretty much all of them have faced revelations of US spying targeting them. If the US keeps pushing like that, they might just find that someone will snap and decide to tell them to go to hell.

It'll be interesting to see if they manage the balancing act of pushing just hard enough to keep everyone in line without pushing anyone too far.