Hyatt has fired up their Nights-After-Nights program this fall/winter. See the web page for more detail, but it is mighty tasty. For example, elite members can get a bonus certificate good for up to 5 nights at _any_ worldwide Hyatt property. Others can get 3 free nights at non-resorts.

As for exchange ratios, if you like to use your points for decent properties, you have to spend $2600 (any rate) to get a free weekend night at a top Hyatt property, $3500 (corporate rates only) for a top Hilton property, not including bonuses.

I'm Hyatt-Diamond, Marriott-Gold and Hilton-Gold (very soon) so I'm very interested in this discussion as well.