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Yes, they are. Hilton HHonors (uniquely among hotel points programs, AFAIK) synchromizes their promos to quarters. The first promo of the year starts in January and runs through March, and is typically referred to as the Q1 promo for that year. The second promo of the year starts in April and runs through June, and is typically referred to as the Q2 promo for that year.

But the nature of the promos can and does change. So there is nothing more to say generally about Q3 or Q4 promos, except that they tend to only be announced officially a couple weeks or so before they start (so the Q3 promo was just announced in the last week or so), but sometimes they get "leaked" a month or more in advance (in the case of this year's Q3 promo, an internal memo to member hotels was "leaked" and gave us heads up on some of the details).

Since the Q3 2011 promo was just announced, it's way too early to be asking about the Q4 promo. Just know that it'll start in October, and be officially announced only shortly before then in September.

But what the nature of each promo is is unpredictable. Last year we had some "stay X, get a free nigh certificate" promos, but none thus far this year, and some think they were tied to the weak travel economy back then and are not likely to be repeated any time soon.

As already mentioned in the post above mine, there's a specific thread for the Q3 2011 (about to start) promo. It strarted out a bit silly (someone asking way too early), and only got useful once that "leaked" memo was posted. (That's why the link above takes you to the middle of the thread rather than the beginning!)