@Gevening, IB needs a TIN (or FIN for Foreign Identification Number if you do not have a TIN) for IB to be able to generate a valid W-8BEN form.
Personally I have been trading without a valid W-8BEN form for some time, without consequences.
However, a friend of mine, with another broker, and without a valid W-8BEN form, was slapped with a tax on realised capital gain. We are obviously talking about US stocks here. He's in the process of getting the money back, his broker thankfully cooperates and after checking with him here and there, the procedure isn't too too complicated.
If you intend to trade US stocks, make sure your TIN/FIN is up to date and that you have generated a proper W-8BEN form. You can do this online in less than 2 minutes.
If you do not have a TIN and you are tax resident in HK, your FIN is your HKID card number. That's how IB (and other brokers/banks actually) told me to populate my form.
What I find a little bit strange... is that IB should have asked you to give a TIN/FIN when you opened your account with them... why is it blank ?...