I'm a longtime rider and work in the industry (currently for a distributor, formerly at Cycle Gear HQ). There's lots of assumptions, marketing hype, misinformation, and conjecture in this thread...
That said, here's my $0.02 on a few things.
Shoei/Arai... good stuff but they've rested on their laurels due to their success for many, many years. Their liner materials and processes haven't kept up with advances from the competition (I'm looking at you, Arai, with your 1990's fabric)
Icon... they've come a long way from the Biker Boyz image of old. The stigma remains but their stuff is (IMO) solid mid-level gear at this point. I have a variant and I love it for around-town riding. The visibility is awesome and the airflow is unparalleled in my experience.
Scorpion... I agree with many, it's one of the bang for the buck. I've been down a few times on the track in one. They did their job well, especially for ~$200
BiLT/Sedici... please don't buy this crap. Even at (a constant 'sale' of) 50% off, it's overpriced. Employee pricing on a $100 MSRP helmet was ~$15. (For reference, a Shoei was around 40% off MSRP for employees... and CG is the biggest reseller of Shoei so they get the best prices)
If you can find it in a style you like... buy a helmet that's DOT -AND- ECE certified. The 2 certifications do a reasonable job of covering all the bases.
A tight fit (that borders on uncormfortable after no less than 5-10min of wearing it) is the key to maximizing a helmet's protection to your dome. If it's slightly loose when you try it on new, it WILL stretch and become loose after 5-10hours of use. You've just lost a good chunk of protection if this happens.
"If I drop my helmet it's done for" Yes and no. It depends on the protective impact layer of the helmet. A small drop from 3ft or less is not going to be an issue 99% of the time. My rule of thumb was whether it cracked the outer shell. A scratch is no big deal. A crack in the shell is like a crack in an egg and is definitely a sign of potential damage to the impact absorbing liner beneath it.
Try on several brands helmets before buying. You could be surprised how much you like a brand you handn't considered prior to trying it on. People often jump on Shoei and Arai b/c of the status... when you could get 90-110% of the helmet for 30-75% of the price.
Read non-industry reviews of the lid. Lots of them. Magazines make a lot of money off of ads from the big players... they're not nearly as harsh on those guys as they might be on a non-advertising brand.
Your head is the one body part you can't replace. Don't skimp.
Current lid
http://i.imgur.com/He6Vt6c.jpg
One of my old lids
http://i.imgur.com/OrmphOX.jpg