I've long been an advocate of hiring a wedding planner to make your big day go smoothly but the popularity of Do-It-Yourself everything now makes a lot of brides and grooms strongly consider taking on the role themselves. Some brides and groom CAN do it.
DIY doesn't always spell disaster - I planned my own wedding and everybody had fun, except me. But there are a lot more wedding planning tools available now that weren't around when I was wedding planning for myself more than 10 years ago.
Still, the kind of job you have, and the general support system behind your wedding, should play the biggest role in deciding whether or not you actually need to hire a wedding planner.
I'm not an advocate of hiring somebody for running things on "the day of" as so many planners advertise now. It's a very bad idea for numerous reasons and I've blogged about it before. End of day, the vendors you've hired have no accountability to your "day of" wedding planner and if they violate their contracts or aren't where they're supposed to be, it's unlikely that planner can do a damned thing about it. Hence the waste of money.
You probably can get away with planning your own wedding if you meet the following criteria (just be honest with yourself when you're considering it):
1) Your job must give you the flexibility to do vendor conference calls during the day. My clients who are in medicine, teaching and the military struggle with this. While a wedding planner might be willing to talk with you and do the planning after normal business hours, your cake vendor, DJ, florist and everybody else keep normal business hours on regular weekdays. It's not their problem if you have a job that doesn't give you time to talk between 8 am and 5 pm. Most will not be available after 5 pm and it's just plain dangerous to do all your planning via email. You will have to take some days off of work and you will struggle if you don't have that kind of daytime flexibility.
2) You are extremely organized and detail-oriented. If you can't even get your regular monthly bills paid on time, and you never have any clue what's in your checking account, and you frequently have to dig for clean clothes for work because you didn't make it to the drycleaners to pick everything up, you can't plan your wedding. You just don't have your shit together enough to make sure that everything comes together properly and you'll end up with a disaster that nobody wants to attend.
3) You have a few friends or close family members who are actually willing to work hard to help you make it all come together the week of the wedding. When you DIY, you have to pick up a lot of things, make a lot of things and deliver a lot of things. There's nobody to do it for you and if you don't plan it out in advance, all hell will break loose and turn you into a Bridezilla at the 11th hour even if that's not normally your personality. You'll find yourself screaming at your fiancé about things that aren't his or her fault if you don't have everything planned and assigned ahead because when the chips are down, you're going to expect your future spouse to bail you out. It's his or her wedding too, right? But if you promised you could handle it all because your fiancé's job doesn't permit that kind of time commitment, dropping the ball in their lap the week of the wedding is totally unfair.
4) You are punctual and do (or have done) project management, at least on some level. Every detail of a wedding hinges on the schedule of events that has the tiniest details documented for the entire last week before the wedding. At our company, we create a Master Schedule for every wedding that the clients never see, although we've talked through every minute during the planning. My ex-cop husband says the only schedule he's ever seen that had more details than my wedding schedule is the U.S. Secret Service on Inauguration Day. We give the vendors a schedule that doesn't have the clients' schedule on it (nobody needs to know when they're coming and going from their accommodations - that's a security risk) and a wedding party schedule for the bride and groom that only includes what they need to know about and be at on time. We give them enough copies for their families and all of their wedding party too. You should create the same sort of schedules if you're planning your own wedding.
5) You have one single individual who will be involved in your planning and WILL TAKE RESPONSIBILITY ON THE BIG DAY. That's the person who will give the boys a hard time if they're not getting dressed and ready for pictures according to the schedule. It's the person who will have your vendor list and check everybody off as they arrive and bring what they're supposed to provide for your wedding. It's also the person who will help run your wedding rehearsal and will tell everybody when to "go" when it's time to walk down the aisle. It cannot be a bridesmaid or your mom - they will be busy on your wedding day. And if things blow up, you can't expect this person to have backup vendors ready to save the day, nor can you give them the responsibility of confirming your vendors and sending out their schedule the week prior. You should do all of that yourself and know that friend is out there making sure everything is happening while you're in your bridal suite getting hair, makeup and nails done for your wedding. 
Realize that when you decide to forego hiring a wedding planner and DIY, you run the risk of having your serene wedding day explode on you because you will be the one who has to triage things if somebody doesn't show up or the venue drops the ball on something. Your point person on the day of won't be able to do the yelling and threatening that must be done sometimes - and don't play, that's the reality of working in a business where there are no second strikes. You get one chance to get every detail of the wedding right and even the best vendors sometimes goof up.
I didn't tackle whether you should try to plan a destination wedding without a wedding planner because that opens up the whole world of questions about how much you actually know about the destination you've chosen - a whole other blog. But if you're getting married at home and you have the qualities and skillset and point person I've described above, you can probably get away without hiring a wedding planner and not have to live with regrets.
Until next time, happy wedding planning from Weddings in Vieques!
Sandy