Trying to 'checkout' the book doesn't seem to be supported for this offer. Instead the splash on the front page points to http://packtlib.packtpub.com/library

This seems to work for me.

You need to first create an account (if you dont already have one).

Offer is valid starting tomorrow (between the 28th and the 30th)

Where I am, its already 28th(GMT+5.30). what timezone?

GMT-5, though I guess it actually is 28th at GMT+0.. Point was just that it still says "Return between the 28th and 30th September to claim your gift", so whoever is supposed to activate the deal hasn't done so yet (and since their office is in England they are probably still asleep)

It is working for me right now--I already downloaded my book free of charge.

Yep working here too. Except for the occasional 502 Bad Gateway that keeps popping up.