Yes, in perl-current with my mro.c stuff (and eventually 5.10), when you change the @ISA of a class or change a method in a class, it only invalidates the method cache of that specific class, as well as any classes which inherit from that class (as opposed to the behavior in 5.9.4 and earlier, where changing a method or @ISA anywhere invalidated all method caches globally).

Also, while in 5.9.4 and earlier the recursive lookup via @ISA is performed every time an uncached method call was made, with the new mro stuff the recursive @ISA parent hierarchy of a class is linearized into a simple flat list of classes to search with no duplicates, and cached. That "linearized isa" cache is only blown on @ISA changes in the given class or its parents, not method changes. So even when you (locally) invalidate the method caches by redefining a subroutine, these @ISA linearizations stay in place, making that first lookup to refill the cache faster than it was before.