This is just my experience, but I hope you find them helpful:
1/ Once you get all the latest updates 3.2.1 (?), is the K1 very reliable? Does App crashes? Does the web browser crash?
The tablet is very stable. The browser will occasionally crash if it's loading a very complex page.
2/ Is there still issue with the lock as I have read on few forum?
Yes, the K1 will occasionally wake up for no apparent reason
3/ Is the sound quality Good? Bad? Average?
Sound quality is OK. I hook up external speakers if I'm watching a video and walking around the house, cleaning, etc.
4/ If somebody has the keyboard/dock, is that a good option?
I have the Logitech BT Keyboard. It is a great accessory. I also have a Kensington BT mouse. It works great with the K1
5/ Pro and cons with the K1?
Pros: this is a very good tablet at a great price. ICS is coming out soon, which should make it even better. I really love the K1.
Cons: Why the heck is the headphone port on the bottom? You can't use it with a folio-style cover/stand because the bottom rests on where the headset would go. To hook up external speakers, I have to turn it "upside down" and plug in the headphones. Not a big problem at all, just a "Why the heck did they do that?"
6/ Is it easy to sync with Macbook Pro?
I don't know. I have a System 76 laptop running Ubuntu. It works great with that to copy over files/music/movies.
7/ Is the Black version a nice option?
If you like black, then yes :)
The camra is OK. The FFC camera is OK for video chats. Right now I can't get Skype Video to work with it, though. Google Talk works fine.
Overall, I recommend the tablet. My wife has an iPad, and we have couple of Android phones, so I'm no stranger to tech. I think that the K1 is very functional and a good value for the price.
Hope this helps.