just curious, can you point me to the forums where you have read this, the 7D may just need a bit of setting up.
The AI Servo can be improved on by internal tweaks, there is a good guide here. I have got some great birds in flight shot, it tracks accurately.
When shooting in Single shot mode, its important to turn off some of the focus areas. Typically I only have spot focus selected. When all 19 areas are active it tends to focus on the closest one, this seems to have caused many focus "issues".
The only issue I have is that with the 70-300L I need to adjust the focus microadjust to +3, otherwise it will consistently front focus. The 50 1.8 front focuses when close, but ok for further away.