I've used YNAB for a while now, and as you can see from my blog, I like the program. My wife and I are not perfect and sometimes we hit financial setbacks that are beyond our control; however, each time we do we stick with our budget. What we see is that we always have enough to pay for bills and get food. YNAB does work, and it works well for personal finances.
However, what about small businesses? Does YNAB work for a business owner?
The answer is... It depends.
It depends on your business. YNAB does extremely well for cash flow budgeting and cash based businesses. If you use a cash based accounting system (you get paid when a product/service is rendered and you pay bills when you receive them) then YNAB is great for you. If you need to have an accrual system, YNAB may not be the best choice.
I have a small company that I run part-time, I sell items online and also do some consulting work. I have QuickBooks Pro (since I am a QuickBooks consultant), but I find myself using YNAB more often. Even though I use both systems, there isn't a lot of work since both programs are able to import and categorize transactions.
I use YNAB to help me keep my cash flow steady and also keep my spending under control. It has the same effect on my company's finances like it does on my personal finances. There are some things that QuickBooks does that YNAB doesn't, like track and manage taxes. Also, YNAB doesn't track inventory. Lastly, the reporting features are lacking when it comes to business reporting, and it cannot do a balance sheet yet.
However, Jesse (the creator of YNAB) is working on improving YNAB for small business owners, so I believe these features will be available eventually.