Originally Posted by yashan
Now I'm echoing TravelLover's question who was echoing Brwsy's question...

Can it be added on top of one of the existing offers?
Reading through the thread, it seems like people are choosing to remove (or are they required?) their 2x and 3x point promotions for the 5/10/15 promo. Is that really the case? Is the 5/10/15 promo worth that?
The answer to your question is (of course) "it depends."

Specifically, it depends on what kind hotel activity you've got lined up and how you like to spend points.
If you work in NYC and are paying $350/ night on average, then in 15 nights, you will have accumulated 52.5K bonus points or 3 free nights. If you tend to stay at bargain properties (i.e., opportunity/ category 1 hotel), then it makes more sense to take the points, as you could get up to 7 free nights that way. Of course, if you prefer high-end places, then you're better off with the certs, as 52.5K points will only get you 1 night in a category 6 hotel.
But, having done a breakeven analysis at a variety of price points (yes, I am a consultant. and a dork), it appears that in general, unless you are determined to spend your points at opp/ cat1 properties, you are best advised to go with 5/10/15 if you have 15 days of hotel stays planned before 7/31.
YMMV, of course, if you have way more nights planned or if you really love them cheap properties.