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50/50 situation for me too.
I used to use the grip 100% of the time on the K10D/K20D since I found that body design too wide to balance properly and the grip squared that out.
On the smaller K-7/K-5 the balance suited me more without the grip, but it's a matter of which lenses at mounted onto the body.
I still use the grip when using long and heavy lenses. Without the grip I find the small camera doesn't balance out the lenses and makes the setup lean forward too easily in my hands.
With my favourite setup OTOH, i.e. when I'm out shooting with smallish primes (esp the various FA and DA limiteds), I *never* use the grip. Ever since the K-7 was introduced it was rumoured to be designed with the limiteds in mind, and I strongly believe that to be the case indeed. To me the K-7/5/5II(s)/3 series is perfectly dimensioned for these small lenses and makes a prefect package for discreet portable photography. As I wrote, for longer and larger lenses such as f/2.8 zooms and tele lenses (and other brand zooms) the camera needs more beef.
Wim