No, I'm not planning to build any aluminum bikes. Sorry. For some context on how I came to write this, check out this MTBR thread.
First, a bit of context: the variety of good quality mountain bikes (both mass produced and custom) available now is astounding. There are an awful lot of good bikes out there both with and without hydroformed tubes.
But putting this in the context of global trade and mass manufacturing in general over the last decade or so, my BS detector goes off quickly when I hear crazy engineering claims about every new technology, *especially* when that technology happens to make it easier or cheaper to mass produce whatever product. Does that mean the technology is bad? Of course not! Cheaper/easier are good things, as long as you're not sacrificing quality (let's not get into whether or not buying everything we own from China is a good idea for now, since that kind of thread just devolves into name-calling in a hurry).
WRT hydroformed tubes specifically, I tend to see them on bikes where I *don't* see much effort made to really tune/engineer the different stock sizes for different riders (ie, same diameter tubes on every size from XS to XL, identical chainstay lengths and BB heights on every size, etc, etc). This generally leads me to believe that manufacturing costs are the driving force behind most of this kind of innovation, not improvements in riding characteristics.
I could of course be wrong. But Occam's Razor says that the best explanation here is just keeping costs down. Of course, that makes pretty crappy marketing copy ("just as good as last year, but 20% cheaper for us to make!"), so if you can make some tweaks to make the frame do a tiny bit better on a test rig, you're a lot better off using that as a selling point, even if the end consumer will never be able to tell.
So I'm not saying hydroformed tubes are bad. I'm just saying they're probably more beneficial to the manufacturer's bottom line than the rider's enjoyment. Just IMO, as always.