Hiya Pom
I'm not actually sure if lane splitting (filtering over here) is legal or not!

I've done it loads and near coppers too.
I imagine you would have to be pretty unlucky to get nicked for it over here.
You'd have to find a copper that:
1. Had loads of time on his hands for the paperwork,
2. Was having a particularly bad day and wanted to take it out on someone OR
3. The coper had his 'quota' of tickets to keep up with!!

The other obvious one is if you were going too quick or doing it dangerously.

I guess it's a fine line between filtering and plain overtaking on the inside (illeagal over by the way to all you Americans who CAN do it).

In slow moving motorway trafic, I'll filter up to around 40 mph with the traffic.
Any slower and I slow too, but still filter.