For anyone who is interested, this is a recent thread on MTBR I started a week ago, in rebuttal to some inaccuracies in a recent BIKE magazine article.
http://forums.mtbr.com/showthread.php?t=95409
The added weight is somewhat of a non-issue as you'll see in that post (depends on how much of a gram shaver you might be). Compared to a typical XT drivetrain, you're looking at 600g of extra heft (~1.5 pounds), with a two pound weight bias shifted to the rear axle.
The total range is equivalent to a compact 24 speed drivetrain with an 11-30 cassette. Within reason, YOU get to pick the highest or lowest gear based on the chainring and cog combo you choose. If you want the equivalent of a 34T bailout gear, you can do it at the expense of your top-end gearing. If you want a super-duper road-ready tall gear, you can do it at the expense of your granny gear.
Compared to a Nexus or SRAM Spectro, the Speedhub is a gem. I ride a Nexus on my pavement bike, and my wife has a SRAM on hers. Both have inconsistant gear jumps, both have crap shifting (the Spectro will click at the shifter but won't even drop into a lower gear if there is any load on the pedals), and neither is sealed against the elements.
Efficiency is on par with a clean derailleur system in the higher 7 gears, and about 1% lower in the lower 7.