This last weekend I finished painting up a Ravenwing Attack Squad. That's 6 bikes, one attack bike and one Landspeeder Tornado.
While you will see the bikers swinging chainswords, their main role will not be melee. I just like the image of them swinging chainswords like a roudy post-apocalyptic biker-gang and really, who doesn't? The option given was to equip them with EITHER a bolt pistol OR a chainsword. In game terms they're virtually identical, since I'd be using the twinlinked boltguns on the front of the bike for any kind of shooting. Given this, they only get one attack. Two if they charge. If they're in combat, however, they cannot leave at their own discretion. They are not considered "vehicles." Due to this, their role is going to be more mobility and shooting. I have equipped my Sergeant with a Power Sword just incase things get hairy, though. Twin-linked bolters are nothing to sneeze at, especially considering that due to them being mounted on the bike, I do not count as having moved when I fire. This means I can fire once up to 24" despite moving. Not bad at all. Add to that a Heavy Bolter on the Attack Bike, and a Heavy Bolter/Assault Cannon combo on the Landspeeder ... and I have a lot of anti-infantry firepower that is extremely mobile.
Oh, there is one added benefit to Ravenwing. All bikes count as having a built-in Teleport Homer. Didja hear that? That means no rolling to scatter when I teleport my Deathwing Terminators in (as long as they come within 6" of a bike). Of course, I plan on taking advantage of this rule. I'd be a fool not to.