I have heard good and bad things of XXXXXX (no need to edit mine ). I think with importing, there are so many delays that are possible that you cant really blame the importer (unless they are obviously doing shit wrong).
Just think of our friend Bxxxx whos car has taken months and months. No explanation why, but the same importer has done cars in 8 weeks as stated by others.
If you use an importer, i think your best bet is to go with someone you trust to get you a good car... dont worry about time limits as there are always unexpected delays with shipping, customs, compliance, import approval etc.
if your really worried about time, go for a private sale. the price difference is very small from what I have seen lately. Dont forget with importing, you usually need a service, + new rego etc where in private sales they have often had good aus servicing and come with rego etc.