In the transition from 4th edition to early 5th and later on in the same edition we saw Nob Bikers going from good to amazing to meh. Quite the sine graph there! While I never run an army with two Nob Biker Deathstars, I always had a smaller unit of these and it really helped in my games. As long as you kept their point cost low enough so you could include other needed stuff in your army they were a must have. They were a resilient, hard hitting, scoring and fairly reliable unit. Very useful in any ork army. The only downside is that they always needed a Warboss on a bike to baby sit them because Leadership 7 would see them running off the board more often than not.
In the MSU meta environment of the mid to late 5th edition (after the Imperial Guard codex came out and especially after Grey Knighs) Nob Bikers just didn't cut it any more. Almost everyone was packing enough high Strength weapons to sent them home and even if they reached enemy lines, charging a rhino or a chimera didn't mean much. So let's see how all this changes in 6th edition.
There are a few factors we need to consider when thinking about the survivability of the Biker Nobs. First of all it's the new wound allocation system. No longer as easy to spread out wounds they way we want to as in 5th edition but with some careful planning we can get results almost as good. Just stick the Warboss near the side that most shooting is going to come from and spread the wounds around using the 2+ Look out Sir. Even if things go wrong you still have a 4+ LoS! on each individual Nob since they all count as characters. One more plus is that you save a few points from pointless junk equipment compared to 5th edition wound allocation shenanigans.
Another big difference is that Bikers are now a real Toughness 5. That's pretty huge. No longer insta-dying from S8 and S9? Yes please! Considering the changes to Feel no Pain rules it means that the bikers will have that extra 5+ save almost every time. On the same note, you will still have FnP in close combat against power weapons and most power fists and that makes a big difference too.
They might have lost the 3+ cover save from turbo boosting but since everything is leaning towards 5+ cover in 6th edition it's nice that they still can have their 4+ cover save all the time. Together with having FnP against most weapons makes them even more resilient than what they were in 5th even though superficially it might not seem so.
If prediction are right and armies become more infantry based then that's awesome because nob bikers munch through infantry and can survive the attacks they will get back. Even if that's not the case and you are up against a vehicle heavy army that's no biggie. Hitting vehicles on a 3+ in close combat makes them excellent tank hunters since they can outrun most of the tanks out there. Power Klaws are AP2 so that a +1 for the vehicle damage table, let's not forget that.Land Raiders, watch out!
Another think to consider is that the whole unit benefits from the Precision Shots and Precision Strikes rules. Even their shooting is deadly now, I'd even go as far as to call them the best sniper unit in the game. Thirty three shots will roll nine 6's on average, that's enough to kill both special weapons and maybe the Sergeant in a 10 man Space Marine Squad. That's even better in close combat since each guy has 5 attacks on the charge. They'll be killing power fists before they even get the chance to swing back.
So, considering their resilience and damage output, plus the fact that they are scoring and their excellent mobility, Nob Bikers with a Biker Warboss are a must (at least for the beginning) for sixth edition. I'll be definitely fielding a bunch of them with my orks and I think they will make an excellent ally for my Necrons and Imperial Guard.