Just studying for the BCMSN and have questions regarding STP.
1) other than backward compatibility, why would you want to use STP when RSTP converges much faster. RSTP has been around long enough that I am suprised it is not a default.
2) The next issue is with portfast. When configuring portfast do you ever notice the little message that IOS gives regarding that it will only be in affect on access ports? With that being the case and assuming you do not lock your ports as access or trunk ports, if you were to plug in another switch that is configured to form a trunk, and it forms a trunk with a switch that has portfast enabled on the port that is now in trunking mode. Would portfast not be enabled now?