I used pre paid Dodo on my last trip (August 2009), I have nothing but compliments, the performance was good to excellent, the value second to none. Dodo uses the Optus network, I think youll find the Optus network has improved dramatically over the past couple of years.
Obviously performance takes a but of a hit at kiddie time, but my home accounts with both Netspace and Bogpond take a similar hit just after school ends.
I paid around $150 for the dongle and the first two months use. I bought mine on line and paid for delivery, had I realised I could have bought from Officeworks and saved the delivery charges.
Dodo allows selection of either hourly of data quantity, I chose 1Gb which I have 2 months to use for $20, during the first month they also gave me 3Gb bonus which I didn't use. On the road we used it every day, I only managed to get through .5Gb over the month.
I did find it necessary to turn on the XP firewall as I was getting some attacks which were crashing IE. Once I had enabled the firewall performance was rock solid.
In Tasmania despite advertising that there was no coverage apart from Hobart, I have been able to get coverage in Launceston and Deloriane, I assume coverage will also extend to Devonport and Burnie. Whilst away we used the Dodo service all the way up the east coast, at Kilkoy on a day trip away from Astrofest and pretty well all large towns on the way down the Newell Highway, e.g. Moree, Hay, Swan Hill, even Pukapunyal.
In my experience, the only places I was unable to get coverage was where I had no mobile coverage (I have a Telstra Mobile BTW).
Personally I wouldn't go with anyone else, the value simply isn't there with the other ISP's and the performance even from Bogpond is no better and Bogponds charges are obscene.
My kids have Bogpond 3G and at 20Km's from Bundaberg my service was as fast as theirs and just as reliable.
I should add that I wouldn't contemplate anything other than pre-paid with Dodo, I had a dial up account directly debited from my credit card, cancelling the dial up account was almost impossible.
I was told by Dodo that the Pre paid can be let expire and topped up at any time.
Dodo also have a 15Gb (a fair amount when you're on the road) 12 month prepaid plan for $139.
I bought my package for my holiday travels, I'm so impressed with the coverage I'm going to pay the $20 each 2 months for work related use.
Plans here
Regarding Bigpond service, since re-locating their Call centres to the Philipines, in my experience (we do a lot of DSL installs for customers) it has been almost impossible to get DSL problems resolved.