[Paleo Pete]

Nikon and Canon both have image stabilization built into their lenses, some others I think. Common perception is that means you pay for it every time you buy a lens. As far as I know Pentax has built IS into the camera from the beginning. That means it works with any lens you use. If you look in your camera's menu, you'll find a setting to turn it on and off, that's because it's built in to the camera before you ever attach a lens.

The camera only asks for focal length when using manual lenses because they do not have the ability to communicate this to the camera. Most auto focus lenses have that ability and the camera automatically "knows" what lens is in use. So you don't have to set it. I think the older A series lenses do let the camera know the focal length, (I think, haven't mounted mine in a while) at least when set to A, but do not have auto focus, just the ability to tell the camera the aperture in use. A series lenses also let you use the rear thumbwheel to adjust aperture. So you don't have to worry about focal length when using the auto lens, only the manual. But when using a manual lens, the main thing that does is allow image stabilization to function optimally for that focal length.

I'd go ahead and use manual lenses any time you want to, if you know how to get a decent exposure, the best way to get proficient with manual lenses is to use them.