I've been using Mint.com to keep track of my budget for almost 5 years now. It tracks purchases on all my bank accounts, categorizes them, and helps me track spending month by month. It's decently intuitive to use, and I've never had a problem with the security it offers. And it's entirely free.
Mint has some features that, to my mind, make it very worth the minimal time it takes to set up. For example, it has sent me alerts several times when my bank charged fees I wasn't expecting. (I was able to get them reversed.) It tracks when my bills are due so I don't miss any. It also offers advice tailored to the way I spend, lets me know when spending in a given category is unusual, and - best of all - makes it really easy to set goals and track progress towards them. Whether you're saving up for a vacation or trying to get out of debt, the easy visual progress towards that goal can be a really helpful motivator.
The best reason to use Mint, to my mind, is that it directs your attention at what you're spending money on. Credit cards make it all too easy to buy without considering the actual impact of what you're buying down the line. Using Mint can help you consider what you really want to do with your money, reclaim your spending habits, and get out of debt that much faster.
Drawbacks: The main drawback is that it does take time to set up and manage all this financial information in Mint. While Mint will automatically categorize your purchases, it doesn't always categorize things correctly. If you buy things from the same places, you can set rules that govern how Mint does its categorizing, but buy from a new vendor and it's likely to end up somewhere unexpected. Keep a weather eye on Mint, especially for the first few months! I've gotten into the habit of checking it every couple of weeks to make sure things aren't too out of place, but checking once a month would probably be a little more efficient.
There are a couple of other minor drawbacks, like the fact that you can't actually move your money around from within Mint, but for me, they're significantly overshadowed by how much easier Mint makes it to track spending from multiple accounts. And it's entirely online, so there's no need to make extra storage space in your house for more pieces of paper you'll never look at after you file them. Now that's a good deal.
