One thing to be aware of is that the BDC has a hard limit of 30 parameters. If you use the BDC as designed, you likely will never hit this limit, but if you are trying to implement insert/update functionality you may encounter this little gotcha. When it happens, you will see the following error message:
The BDC Meta Man tool has a write-back feature that adds custom actions for inserting and updating. The tool will create an insert action and an update action, and add a parameter for each selected column.
Beware of the 30 parameter limit when designing BDC solutions.