Yes there is some challenge to Australia in tests but quite frankly only from India and to a lesser extent England and SA. These are the only teams that have won test matches against Australia in the 21st century. I am afraid the other sides have not been able to match them in tests over the past 8 or 9 years. But now with McGrath, Warne etc. gone, the Aussie bowling does not look so menacing and maybe teams like SLA and even Pakistan have a chance against them.
I was looking thru test stats and India have won 7 tests and lost 6 in 19 India-Australia tests since 2001...
And if you thought only Hayden (47 runs in 4 innings @ 11.75) was struggling just take a look @ Lee's bowling stats in the current series
71 Overs - 9 Maidens - 249 Runs - 1 wkt - Bowling ave: 249.00 - SR 426.0