This is in part an update post in connection to an ealyer Post Blog  faq-about-the-mekgineer-s-chopper-mechano-hog 

Knowing that with Patch 3.1  a number of changers were most likly to be made. Having had a week to test and learn all the pros and cons. I can think of.  I now shall share them with you.

The Cons being, the K3 parts are still 12500k gold to buy. Wish they were cheaper,as the tank bike effect has been removed.

You can no longer do a vertical drop from the Dalaran sewer pipe and live upon impact, or off any other high ledge and live, So in this respect this is a total nerf, of one of the most fun things about the bikes. If you are riding shot gun in the side car, do not except invitation to join a battle ground. First leave the side car then except, Other wise you will either fall through the terrain, and end up dead have to res at Grave yard, and suffer the shame of deserter, or you may be ported to a place anywhere in the world, or you will find yourself in a weird semi zone of the Battleground yet are unable to participate in it. 

THis is largely due to the fact the bikes have been re scripted to be an ordinary mount, taking ordinary mount abilities.

THis is were some of the Pros of the bike come in.

One with automatic dismount option of cast spell, now means you can ride into battle and begin to engage your battle ground opponents. ( without having to right click and dismount via the dismount button.

You will no longer be dismounted when you pass through a world portal, or enter into water, by the way the bikes make a very cool and quite fast boat.

Yet to me the best part of having a bike was nicly summed up in a comment by 

Brisson "Exploring whole azeroth on my bike with Steppenwolf on the radio."

So there are plus's ( though I do miss my tank bike) and the best of these is having a cool bike you can ride round with your friends have a great time doing it. and  classy mount to do so.