We have been timeshare owners since 1996. A rough estimate of our cost when you include all of the maintenance fees, exchange company fees, etc is about $100 a night. There are times and places, such as Orlando in the off-season, where I could probably rent for that amount or less (don't forget to include the taxes on rentals when you're comparing).
On the other hand, there are other times when we stay somewhere for FAR less than the going rate. Nantucket Island, Boston, England, Scotland, Hawaii. We've stayed in some pretty incredible places, usually in 2br units since there are six of us, for huge bargains.
There are lots of ways to maximize your ownerships, and the advice above to visit TUG is an excellent one. I've become a much more informed owner since discovering them. For example, we own a three bedroom lockout at Mystic Dunes week 52. This year, we'll be there starting 12/29. Easy to get the high demand week we own. Just had to make one phone call. We'll use the two bedroom part and deposited the one bedroom part with an exchange company. So for about $1000, we'll have this week and another one somewhere else at another time.
If we weren't tied to school schedules, we could/would travel off-season and might make different decisions. For us, though, this has worked out great. Our only problem is that we own six weeks which really generate nine - ten total vacation weeks and we just don't have enough time off to take them all. Five or six weeks a year is all we can manage. I plan to list a couple of our weeks for sale after the first of the year, but I can't imagine ever giving them all up.
Sheila