First of all, yes, that's always the argument I hear. That and people not taking Switzerland seriously since it's anyway just Nazi gold and gangster banks enabling us to do what we do, right?
Online voting tools could definitely change the cost as well as the legitimacy of running a superpower scale direct democracy. In Switzerland we largely handle it through voting by letter and every commune handles the counting - technically it's certainly possible to have fraud at that point, however at least I'm not aware of any case where a people's vote would have been faked that way.
Anyway, for larger scale voting I'd have a look at this TED talk: http://www.ted.com/talks/david_bismark_e_voting_without_frau.... E-voting combined with tokens on paper seems to be the winner for me.
But don't forget, the stability of the Swiss system doesn't only come from its direct democratic nature, I'd say the principle of proportionality applied to the government, as I mentioned above, is at least as important. In Switzerland this ensures both checks and balances as well as a government that represents the current political views of the parliament. Also, it lead to a multi-party system with 5 larger players and dynamic coalitions depending on the actual issue. Together with the constant fear of the people's vote this handles most issues quite neatly - even if the process tends to be a bit slower, the output of 'bullshit' is much lower than the things I read from abroad if you will.