First Let me start with a couple disclaimers:
 This is my interpretations of 6th Edition, the Space Marine Codex, and Bike Armies as a whole 13 games in, including several Nova Qualifier / Beta games.. I am 8-3-2 using pure codex SM, BA, and also SM’s with IG / BA Allies.
I welcome 6th, I like change! The challenge of adapting to new rules, the introduction of new tactics, all have me excited. I have mixed feelings however on Bikes in 6th.

Second a unit breakdown highlighting the major changes and what I have seen.
 To keep it brief I am summing up what I have experienced and if you want details justifying my position post and I will respond.

Landspeeder:
Moderate decrease in survivability; 5+ Jinx save is outweighed by hull points. Previously in 5th light arms fire or a poor penetration would result in a stun or immobilization which would have little effect. Two Bolter glances making it through now kills the model.  
Landspeeder Storm:
This breaks my heart; CRIPPLING decrease in survivability; Now nearly useless with no first turn and reserve assaults.  Due to the low threat commonly in 5thsmall arms would target it, infrequently heavy weapons, and glances / low rolls penetrations would in the end mean nothing.  Paired with open topped and the new table they (I used two to three) they were one hit killed in every game I used them in.
Attack Bike Squad:
Marked increase in usefulness and durability with base toughness 5. Paired with outflanking and +2 on the table from Melta weapon they are a cheap and exceptions replacement for the failing LandSpeers.
Scout Bike Squad:
CRIPPLING decrease in usefulness and survivability;  No outflank or first turn assaults. NO SCOUT TURBO-BOOST. Turbo-Boost save decreased to a 4+. IMHO way too expensive for a screening unit (often debated in 5th).
Vindicator:
Significant increase in usefulness; With the rise of terminators both as allies and core and the major change in blast templates I think they are very worthwhile.
Thunderfire Cannon:
My Pride and joy has received both a major boon and a serious Achilles’ Heel. Given two wounds and toughness 7  in 6th, vs standard incoming fire it is much more survivable. Wounding even the Techmarine is much more difficult now ! However poisoned attacks now threaten it (vs having a 66% chance of being ignored), making the weight of fire from DE army a threat like never before. Two other things to note… First the change in blast temples make it a serious threat to light vehicles. Second there was major change in how blast templates were placed (Compare the rules and photos) resulting in it being much harder to hit more than two models unless tightly packed.
Dreadnoughts:
As good as before if not better than before, Glances only matter with the 3rd and they are critical (DakkaDakka) anti-flyer support
Terminators:
Serious Improvement in durability, I mean read the interwebs!
Space Marine Captain on Bike:
Overpriced, (Compare to Coteaz for example) under powered. See Space Marine Bike Entry.
Khan:
SERIOUSLY Overpriced, and received a major blow to his usefulness. The change in power weapons (Khan’s is clearly a special power SWORD) renders him nearly worthless vs Terminators. The Change to outflanking assaults cripples the build. Loss of Init bonus for Furious charge greatly impacts the order of attacks weakening assaults in support of Space Marine Bike Squads. The Lack of Skilled Rider (Come on, really!!?!), which would help balance the multiple nerf bat blows, reinforces my impression his multiple faults. Additional notes see Space Marine Bike Entry.  
Close Combat Scouts:
See Landspeeder Storm / Scout Bikes
Scout Snipers:
Especially with Telion, they are much more impressive now. The ability to pick out special weapons is exceptionally helpful.
Space Marine Bikes:
Significant Decrease is usefulness. Decrease in survivability not outweighed by Jinx IMHO. Focused Fire removes a common tactic of shielding Bikes by placing some in cover. Removal of Closest first means Melta / Plasma gets snipped out early and often. The Inability to hold multiple objectives hurts the ability to win objective based games due to low scoring unit count / high cost of bikes. The Disorganized assault change hurts their ability to multi-assault.  Inability to assault after outflanking reduces the ability to get “stuck in” and survive. Reduction in cover save from Turbo-Boosting reduces longevity. Finally the change to combat squads cripples their flexibility. Weaker in assault. I could go on, but I will let you discover more.

Third, Tactical thoughts from the games.
Aegis Defense Line w/ Quan-Gun:
4+ Cover for all behind it, and critical interception shots on flyers. It suffers from the same weakness and strengths as the TFC. Assuming this and the Bastion go over well at the Nova I think it’s a safe bet we will see this introduced into common use in the tournament circuit.  I think it should be included in all lists, especially over 1750.
Allies:
Becoming a bigger fan as it helps balance “some” weakness in the SM book. Solo Codex still has a lot of power however, but has dropped a tier on the ladder of potency.

Final Thoughts…
As much as I love Bikes I am leaning more and more to their retirement from common tournament play. For 310 points (9 man, M+M+MM+PF) you can buy a nearly unbreakable IG Blob Squad that will outshoot, out contest and destroy the Bikes in close combat. The addition of a new Codex (Dark Angels maybe???) reducing the cost of bikes or introducing new special characters with Stealth, Skilled Rider or a new special rule might also breath life back into Space Marine Bikes.