This card is DEFINITELY overrated. Why? Because A. Elf decks have MASSIVE mana accelleration (Let me think... Birds of Paradise, Llanowar Elves, Gaea's Cradle, Rofellos, Llanowar Emissary, and Priest of Titania, just to name a few), and nearly all creatures in elf decks are really cheap. Sure, piper can play more powerful green cards (or any cards, if your running multiple colours), but there is no point at all. Why? Well, with all of the extra mana floating around, you could basically dry cast anything, and there'd be no point in piping it. Also, instead of relying on powerful creatures, rely on small creatures and pumping of said creatures. Such as with Elvish Champion, Coat of Arms, etc, which all work in an elf deck. Also, there are some great enchantments and equipment for elf decks (Blanchwood Armour, Umizawas Jitte), powering them further. Combine these factors with the fact that you can pump them even more white 1-turn instants (Giant Growth, Might of Oaks, Berserk (If you've got the cash)), to make them stronger. I'd think doing all of this makes more sense then getting 1 or 2 massive creatures into play, don't you? Or, you can just forget this and make an generic "elfball" finisher, where you use your 20+ mana (think about it. Gaea's Cradle gives you 1 green mana for every creature under your control, Rofellos gives you 1 green mana for every forest you control, and Priest of Titania gives you 1 green mana for every elf in your control. Combine this with the several forests, and the Llanowar Elves and Birds you have floating around. Suddenly the 20-30+ mana seems plausible now, doesn't it?) on a fireball. Instant death. What do you think of your little elvish piper now?
Well, maybe I'm being hard on the Piper. It is a pretty good card (For example, as early as your 3rd or 4th turn, you can get a Serra Avatar into play (with the right accelleration, and an Elvish Piper), when your still at high life), but is much overpowered by generic tribal elves.