Like others have said, look before you leap- take the time to learn and make sure you know the pros and cons. First and foremost, make sure you've vacationed in one and made sure it suits your lifestyle. Don't get me wrong- there's plenty of positives- larger space, kitchen for breakfasts, possibly packing lunches and/or grilling at dinner, privacy, ability to travel/invite family/friends, laundry facilities making packing easier or with younger children, etc.. But there are some negatives that bother some people- while resorts are well equipped and have great facilities imho, others would argue that it's not 5 star luxury accommodations, you have to get your towels for by the pool/beach, have to secure your own chaises by the pool/beach (although most resorts have them set up and available for free), and they won't generally have cushions and terrycloth covers. Food and beverage service at your lounge isn't the same as staying at the Ritz, etc. No one is going to bring you bottles of ice water, for example.
Just so no one is rolling their eyes as they read this, since most of us here feel that stuff is superfluous, I'm not in any way suggesting that these are deal breakers, but I know some people regret their decision to purchase because that's a level of luxury that they expected. For the vast majority, the extra space, etc. is well worth the trade off, but I know I have some family members who clearly feel that it's kinda slumming it

, and have friends who wish there were more amenities.
Just so I don't leave you with a negative vibe, our only regret is not having discovered this before our youngest was in grad school. Would've really enjoyed traveling with more space and not hearing the "what do you want to do for breakfast" with the ensuing angst before starting each day. You'll read/hear comments like rent/don't buy, but ownership is beyond a financial investment; there's lots of arguments that it really isn't a financial investment (although we've saved thousands over the years). It's a lifestyle investment; for most it changes the way you travel, whether forcing you to take a vacation since there's the psychological impact of not wanting to waste something already paid for, or the ability to take along family and friends. It's the ability to grab an extra week or two, or even to help out friends with a last minute getaway that you book for them in Interval. Most will concur the real investment is in family and creating precious memories! Many years ago we had a family vacation booked during our daughter's intersession, to celebrate my parents' 60th anniversary. I saw an inexpensive week in a 2 BR in November, 2 weeks before their anniversary, as a Getaway in II to a great resort in a location which I knew would be great, and we decided to just take them for an extra pre-anniversary celebration. The four of us shared a special week, full of memories that will last a lifetime. Shockingly and unexpectantly we lost my Dad a few weeks after their anniversary, and never made it to the planned family celebration, but will forever cherish the memories of our last trip together, which we definitely wouldn't have even thought about booking if not for our ownership.