About 6 months after buying my 7D, I got the associated battery grip for it, and my feelings on it are mixed...

As others have said, at times, the duplicated buttons for portrait orientation can come in extremely handy. Not only do they allow you to operate the camera in portrait mode without craning an arm over to reach the normal buttons, but because of this, you will maintain a much much steadier grip for stability.

Another positive aspect is that the additional 'bulk' of it, really balances out any larger lenses that you may use. This is especially noticable with telephoto lenses such as the 100-400L, or any 200mm+ primes.

Having room for 2 batteries is also fantastic - I know you said you didn't have this problem, but for me, if I'm at an airshow for example, I know and have confidence that I can shoot all day, and fill my memory cards well before I have any issues with batteries dying. Also, if caught in a pinch, the battery grip allows you to use AA batteries to power your camera too.

So, the pros are that it allows easier, steadier camera use in portrait orientation, balances the camera well, and gives you longer shooting time with an additional battery.

However...

Most of the time, in normal every day shooting, where I just want to head out with the camera, I will take the grip off. I'll take my 24mm and 50mm lenses only, and camera with no grip, and "go light". After any amount of time using the 7D with grip which is a fairly weightly bit of kit; to take it off and have only the basic body with one prime lens (especially the 50!) is so refreshing and almost empowering. It encourages me to take it out when sometimes if it had the grip on, I may not.

So... there are pros and cons. I'd say to summarise that it's DEFINITELY worth having one, even if you only find yourself using it occasionally.