I'd like to start my review with 2 statements:
1) for the price you CANNOT get better value for money
2) build quality out of the box may be bad, but with good maintenance and checks before first ride you wont get a nightmare story like you often see.

It is very true the bike vibrates, in my case audibly from the exhaust between 5-6k rpm, a common fault caused by the exhaust not being tightened when building. whether they leave bolts loose for shipping intentionally I dont know but as many good reviews have pointed out, if you want yourself and your bike to survive then make sure bits are tightened and use nylock (or similar).
There are a few common faults with these bikes:
* vibration causing bolts to loosen (shearing is unlikely unless the bolt is over-tightened)
* totally rubbish standard battery and spark plug (replace upon purchase)
* lighting electrical fault (my answer is simply make my own circuit to stop blowing the bulbs)
* the bike rusts very easily (especially in winter even if garaged)

Other than this most faults are a product of poor maintenance or vibration.
These aren't "bad bikes" but you have to appreciate them for what they are. Mine tops out at 65mph but happily sat there for 2 hours (Manchester to Birmingham). This isn't a race bike (though I've read its not too bad off road if properly built), its a 4 stroke so wont accelerate as quick as other 2 stroke 125's (however they tend to blow up.. trust me :D).
If you treat the bike well then you'll have only few problems which you could expect from any bike.
As a note I would recommend replacing some consumables upon purchase (eg brake shoes/pads, spark plugs, battery).

overall I'm happy, I have had to do work on the bike and there are little niggles but in no way do I regret buying it!

So if your on a budget, looking for something to learn on that can handle you dropping it, or even if your wondering how to do work on a bike. I'd strongly recommend this bike.
given the choice between a new chinese bike or an old 125 with however many previous owners trying to destroy it, I'd pick the chinese everytime.

Happy Riding