I asked the same question a while back. Here's a link to the responses I got, some really good info: APUG.org: Cross processing colour film
I've experimented with Fuiji Provia and Velvia in C-41 and I have to say, I love the saturation and contrasty appearance. I haven't tried Ektachrome yet.
I don't know about the pro-labs in Australia, but the labs I have used in the states have been OK, except for one - Gamma in Chicago - where the owner tried to tell me that cross processing 'screws up' his chemistry and I would have to pay 10 times the C-41 list price! Afterwards, I went back, where the 'regular' counter people took it in and processed it for me at the C-41 listed price without blinking an eye. It's like any beaurocracy - hit and miss, depending on who you get, and how much they know to be dangerous.