In short:

Virgin Blue - nothing to worry about. They're closer to QANTAS in Australia than they are to Jetstar or Tiger. I do the vast majority of flying with them and have never been checked for weight restrictions.

They're a fantastic airline and you'll really enjoy flying with them.

Jetstar Australia - They're a lot closer to being a low-cost carrier than Virgin is, and aren't as good, but still, I wouldn't be too worried. Have flown with them a few times and no checks.

Jetstar Asia - Have flown with them once or twice, was checked once. I'd stay under the limit just to be safe, mainly because there never seems to be room in the overhead compartments.

Tiger (both Australia and Singapore) - they will most likely check, and they will probably give you grief if you're over. Lately they seem to be turning the screws a bit on their baggage rules, especially with carry on.

One way to avoid scrutiny on all these airlines is to use web or kiosk check-in. Nobody's going to ask you any questions if you can go straight to the gate!

Happy flying!