If that was the whole point of gfxCardStatus, I wouldn't have buried the settings under the Advanced tab in preferences.
Power source-based switching was removed because a) it has never worked 100% properly, and was causing an unbelievable amount of problems for some people, and b) I get several hundred support emails about it per month. I just don't have the time to deal with that anymore. Rather than spend a ton of time trying to fix it, it's being removed altogether, because it's largely unnecessary if you're on 10.8 at this point.
gfxCardStatus is, first and foremost, a diagnostic utility. The recommended way to use it is to just start it up, and not touch anything – leave it in Dynamic Switching mode. That way, you know when something is draining your battery, and you can send a note to the developer(s) of those apps, and ask them to fix it (unless the app has a good reason to use the discrete GPU, like Photoshop, Keynote, iPhoto, games, etc.).
Having Integrated Only mode available is convenient when you really need to squeeze some extra battery life out of your machine, but it's not what you should be running in 100% of the time. There's a good reason that OS X's automatic graphics switching is on by default – so that there can be a relative balance between graphics performance and battery life. It just so happened that in the 10.6 and 10.7 days, it was mostly the former, because nearly every other app caused the discrete GPU to come on. In 10.8, that has largely been resolved.
tl;dr – use Dynamic Switching.