The one Siri-like thing Speaktoit does is it displays what it heard from you. I can tell immediately if I'm going to get the results I'm looking for. With Vlingo and GV, I have to wait to see what will happen.
The bottom line is that Siri is one part parlor trick and one part Google Voice. The only real world thing it can do that GV doesn't is schedule appointments with prompts. The rest of it is amusing, but not practical and will probably only be used by a few people. Until they lock down that interface where the voice recognition is 100%, it's just a cute toy.