As long as Gary Walsh does not read this post, please address me as "The Hunter Semillon King".
2004 was the greatest vintage the decade for aging Hunter Semillon, although reports suggest that 2008 could be as good.
Yes there will be great ageworthy Semillon made by many producers in 2008, but if you were serious about aging Hunter Semillon and you did not want to take risks, call up the Tyrrell's cellar door, become a Private Bin member if need be, and buy a case of the 2008 Vat 1 for $25 per bottle. Drink one or two now as they will be great in a different way, then wait 8-10 years then drink one every summer. I am just about to crack open the first of my 2000 Vat 1's soon.
Something that will be a little more expensive but you will reap the benefits faster and it will still be risk-free, is to buy the 2004 Meerea Peak "Alexander Munro" Semillon (it is soon to be released or just has been). This is the greatest young Semillon I have tasted (a few years ago now) and will age and continue to improve for 20 years.
Buy some of the Mount Pleasant Elizabeth Museum Releases in order to experience aged Semillon, although watch out for the effects of oxidisation. It is best to experience these at cellar door if possible, or keep the receipt of a retailer. I would not buy these from auction.
Adair
Wine is bottled poetry.