What is the ideal or optimum drinking temperature for beer?
The ideal serving temperature for beer is derived from its method of fermentation. Bottom fermented beers, like lager or pilsner, tend to be best served cold, top fermented beers, ale and stouts, are better slightly warmer. This much seems to be written into our DNA, and of course much is left to personal preference. A stubby holder will certainly help keep your beer in the optimum temperature range for longer!
Another guide that may help though is the colour of the beer. Many enthusiasts indicate that lighter (in colour) beers are best enjoyed cold and the darker the beer the higher the serving temperature should be. Stout for instance can best be enjoyed at 11 - 13°C, and like red wine, should really be served in a goblet. Likewise lager's flavours are best enjoyed at 5 - 7° C and should be served in tall glasses (tall, thin glasses reduce the amount of heat able to be gained by the drink).
Aside from looking lush, the job of any can or bottle insulator is to keep the drink in these optimum ranges for as long as possible, so all those subtle nuances that beer alchemists labour over can be best appreciated by you!