I ditched my Croconaw in SoulSilver recently, giving me a team of Victreebel/Scyther/Ambipom/Corsola/Misdreavus/Mamoswine. I feel like Feraligatr would be more useful than Corsola, but she's so damn adorable. ;___;
Apart from that, I usually have no reason to ditch my starter. I usually like them too much/have no other option in mind.