It's a good thing if you're not in a position to buy today. For instance, if your credit scores aren't where they need to be, or you don't have the necessary cash. (Yes, you can buy FHA with just 3.5% down, but you really do need some cash reserves beyond that.) However, then you'd use those 2 years to improve your credit score and to save up some cash.
It's a good thing if you're concerned that values might drop further. Example: Let's say you're interested in homes currently selling for $150,000. But you think they might fall. You do a lease-option for, let's say, $150,000. If prices fall to $125,000, then obviously you don't want to buy for $150,000. You just walk away at the end of your lease and you haven't lost $25,000.
It's a good thing if you think values will rise substantially. That's probably not likely--a local Realtor can help you with that question. But, using the example above, if you're concerned that while you might be able to afford $150,000 in 2 years, you might not be able to afford $200,000, then you can lock in the $150,000 price today. (Same thing with the lease-purchase described by Michael and Tom, below. Except with a lease-purchase you're locked into purchasing.)
Let's look at the other side.
It's not so good if you're in a position to buy now and you plan on living in the property for, perhaps, 6 years or more. Interest rates are great and prices--when compared to a few years ago--are very attractive. Still, there's a possibility that prices will stay flat, or even decline, for a few more years. However, if you're confident you'll be there for a while (I said 6 years, but the longer the better), then there's sufficient time for the market to stabilize and even recover.
It's not so good if you find the ideal house today. Now, there are always going to be houses coming onto the market--plenty of them. But your selection of properties is going to be much narrower with lease-options or rent-to-owns than with straight purchases. You really don't want to just "settle" for an adequate lease-option property rather than purchasing a home that really meets your needs.
It's not so good if you're dealing with real estate professionals (Realtors, lawyers, etc.) who don't understand lease-options and rent-to-owns. Even from the answers below, I can see that some of the folks do understand lease-options and rent-to-owns. Others . . . not quite as confident about them. Further, there are some special protections you want built into the agreement to protect you. A Realtor or lawyer with experience in the area will know what they are (for instance, protection against the owner not paying his/her mortgage, and protection for you in case property values drop).
So, unfortunately, the answer to your question is "It depends."
Hope that helps.