Wiring a usb charger directly into 12V DC?

[MMM]

Not a good idea. I'm not totally sure how a motorcycle would be set up, but i've heard of people frying things by hooking directly into electrical systems on cars, boats, etc. because the alternator created a huge power spike for one reason or another. The engine starter also has the potential to create some weird issues. Something regulated and well isolated is definitely the way go if you're connecting to any sensitive electronics.

Rubbish, if the alternator or starter did this it would also cause problems for the rest of the bikes electrics.....my qualifications is an electrician.
If the alternator regulator failed by putting out higher voltage then the whole electrical system will fail for sure.
Your here say of people frying things could be true due to the fact they are not knowledgeable in what they are attempting to do..... hence leave it to some one who is qualified.