I purchased this back in March from Sam's Club...

http://www.amazon.com/Unknown-The-Upside-down-Tomato-Garden/dp/B0018RIGT6/ref=pd_rhf_p_t_1?ie=UTF8&qid=1243866850&sr=8-16

In my experience, the tomatoes grew in a J-shape as you're describing, but, two months later, they are doing just fine. In fact, they are overtaking my deck (I made the mistake of planting indeterminate tomatoes...next year I will plant Roma, I think.)

My plants are quite large with several golf ball sized tomatoes and the stems are nice and thick. I have been very pleased with this thing (despite the negative reviews on Amazon!)

I have never grown anything upside down, but it is my experience that nearly all plants reach for the sun, so I think, but am not sure, that this is "normal" for this type of planting.

Check over on the Growing Tomatoes forum (linked at the top of this forum's page) as there are many discussions running on these. In fact your exact question is discussed there. ;)

Dave