We've owned at Divi St. Maarten for about 20 years. The resort is in a beautiful setting and is generally well maintained. It isn't Marriott or Hilton quality but the units are very spacious and have great views. The resort was badly damaged by the big hurricane 20 years ago, but to Divi's credit they worked hard to redo timeshare buildings, tore down and rebuilt the restaurant building, etc. and generally brought the resort back to great condition. We had a special assessment five years go or so to renovate our unit, but the redo has been worth it.
One of the issues for Divi SXM is that they originally sold with a contract that didn't require owners to pay a maintanence fee if they didn't use their unit that year. It worked fine at first, but became an issue when many of the original owners aged and didn't want to travel every year. The special assessment did push some of them out, but there are still some of those contracts around.
Divi is an RTU resort, so we have a 40 year ownership, with the ability to accelerate the use of the last 10 years, if we want to stay for 2 weeks. They are now selling a points or club type system, I think, but we haven't gone to an owners' update for a few years because we aren't interested in changing our contract.
We have traded within the Divi system to Aruba, where Divi owns two resorts and is the manager for a third (Divi Phoenix). The internal trade works well, and if you call as soon allowed it seems units are generally available. We belonged to RCI for a while, but our week is in a lower season for SXM so our trade value was crummy. We got a couple of decent trades but decided we're mostly interested in going to SXM for at least a week every year. Divi just switched to II, so we just got a free year's membership from II.
Let me know what other questions you have. There is a Divi timeshare owners group on Yahoo as well. Not sure if you can join as someone interested, but the group publishes a list of owners looking to sell or rent units, which might be helpful if you're interested in purchasing or visiting one of the resorts to check them out.