I have to disagree -- I just bought the K50 with 18-135 deal, and it's awesome! I came from a K200D. I figured the 18-135 would be a keeper (it's received poor "technical" reviews, but everyone who's mentioned it has really liked it) and I'll be ready for a new camera body in a couple of years (as opposed to seven) since Pentax has had a habit of deeply discounting discontinued bodies in the past. And not just for the alliteration.
If I figure it right, I got the K50 for about $250 and the 18-135 for about $400. Good deals all around in my book. If you don't need 24MP, the noise performance is about the same in low light and the AF isn't better enough for sports on the K3, but either is miles ahead of the K200D. I know Adam said the K3 will "last you for a very long while
." I respect his opinion tremendously -- he knows far more about photography and has a lot more experience than I do. However, I view this as a philosophical difference. I think of modern camera bodies as essentially disposable. Improvements come so fast, and now even Pentax is sluggish to update older bodies to accommodate changes. (For instance, if I ever purchase the 150-450, it won't work fully with either body I have now.) I think the wiser way is to determine if the body will do what you want NOW and buy cheap.
If build quality is important to you, the K50 will be a disappointment. I believe the K50 is reasonably well built, but it feels like a toy next to the K200D despite the fact the two bodies occupied the same relative places in Pentax's lineup at their respective times. But the K50 does have a lot of nice new features, a few that the K3 doesn't have that were important to me (AA batteries, anyone?), and a tremendous improvement in operation over K200D (esp. autofocus and operating speed).
There are a few odd nitpicks I have about the K50 (again, only having used the K200D in the past), and the 18-135 has a couple of odd things going on compared to my other lenses, but in my opinion none of them are show-stoppers. I thought about posting about it in the K50 forum, but it's an older body/lens combo, so I figured no one else cared.
I've had it out shooting a couple of times and with the 18-135 it is a lot of fun! With the improved AF speed, it makes some things possible that were really difficult on the K200D.
Whatever way you go, I hope you enjoy it.