I was on the west coastish the presentation was in Park City. When you say caveats what are some of the caveats? The sales person did not bring any up (not surprised).
By caveats, I really mean there are a lot of variables that might make one system better over another for your personal situation. For instance - where you like to vacation, how often you like to vacation, your ability to take last minute trips, and other factors.
The two systems are completely different, and as bbodb1 mentions, Club Wyndham has a bigger presence in the eastern US, and Worldmark has a bigger presence in the western US.
bbodb1 misstates my point however on where you live being the determining factor. What I said is that it is a no-brainer if you live on the west coast. That is because WM has a variety of cash booking options that it would foolish to not have available to you if you lived within driving distance of their CA/WA/OR/UT resorts. I am not saying that someone in the midwest or east coast should not buy Worldmark, only that it is the superior choice if you live in the west. A similar cash-booking option is not available in Club Wyndham, so perhaps bbodb1 is not aware of how much more value it adds to a WM membership.
I would also disagree with bbodb1 on that if you buy Club Wyndham you can still book WM resorts. This is possible, but is very difficult in peak season - if not impossible at the best resorts (ie. West Yellowstone or Depoe Bay in summer). And this benefit (called Club Pass) is only possible with a developer purchase - which is not worth the cost IMHO.
Bottom line - WM is far more flexible, and has cash booking options (Bonus Time, FAX, Inventory Specials) that do not exist with Club Wyndham. Also with WM you have the ability to exchange with both RCI and II, where as with Club Wyndham you are basically limited to only RCI (unless you own at a few select resorts). Club Wyndham is less flexible, but has more options on the east coast.