Re: My 17 month old is not talking.
I agree - if he understands what you say and responds to noises (in other words, shows no signs of a hearing problem), there's probably nothing to worry about. My older DS hardly said any words or phrases until he was almost 2. Then in a period of about a month, he was speaking in full sentences. We moved to Germany shortly after his 2nd birthday, and by the time he was 3 he was fluently speaking both English and German.
If he still isn't saying much in a few weeks, and you still have concerns, just bring it up with his doctor at his 18 month check-up.