Well, I've never had any trouble with "make oldconfig." In fact, I backup the ".config" file whenever I make a new kernel to another place. Then, I unpack the new kernel and drop the .config file in place. The only time I ever do the configuration from scratch is if I were to go from one major version to another. For example, from a 2.2 to a 2.4 kernel. Otherwise, I go ahead and run through the "make oldconfig" and answer any questions it asks. I then run "make menuconfig" to make sure everything is still in place. I then do the rest. Never a problem yet.
