I thought I'd share my recent experience of trying out a 30-minute boil.
I do a partial boil of 2.5-3 gallons and use extract for at least 80% of my fermentables (sometimes I partial mash with up to 2 lbs of grain).
Since December, I've been doing 30-minute boils to try and save energy and reduce the amount of steam that condenses on all my windows.
I scaled the hops in my recipes to try and hit the same IBUs. Left the grain bill unchanged.
First Batch: Dark Mild. All hops were originally scheduled as 60-minute addition. I scaled and converted to 30-minutes. This beer had some problems, but not due to the 30-minute boil. It came out a little thin tasting and lacking in body. I think that was due to the low amount of extract used. In any case, there was smooth bitterness to balance the malt and no hop aroma or flavor. It was a malty beer that was a little thin.
Second Batch: Blonde Ale. I try to get as close to Munich Helles as I can with ale yeast. The original recipe called for one 60-minute addition. I did mine at 30, and again did not have big hop aroma or flavor. Just a bitterness to balance the malt. This beer turned out really nicely. Delicate and balanced.
Third Batch: Cascade Pale Ale. I was going for the alcohol content of an American Pale Ale (~5%) with the hop flavor and aroma of an IPA. This time, I did a first wort addition with some of the hops, and added the rest using a DFH 60-Minute style schedule (throw a couple of pellets in every few minutes). I calculated the additions using 5 minute intervals, to try and get the IBU in a certain ballpark. Dry-hopped as primary was winding down. This one is the best beer I have ever made. It's on the bitter side, though not at IPA-levels. There is great hop aroma and flavor all the way through. The hop flavor is not super-complex (maybe even a little 1-dimensional), but I think it really comes through as a Cascade beer.
I've had a bunch of people, including my local home-brew club, taste some of these. I got some good feedback, but where the 30-minute boil is concerned, here are the highlights:
1) Nobody said anything about even a trace of DMS, cooked vegetable, green apple, etc. flavors.
2) Nobody said anything about inappropriate hoppiness for the mild and the blonde ale.
3) Everyone agreed that these beers were balanced and drinkable (notwithstanding the thinness, and some apricot aroma in the blonde ale from using the wrong yeast).
So if you're thinking of reducing your boil time, I say give it a shot.