Damn, I just wrote a big post explaining my tests on the iPhone, but I timedout and lost it <img src="smileys/smiley19.gif" border="0" align="middle" /> <img src="smileys/smiley19.gif" border="0" align="middle" /> <img src="smileys/smiley19.gif" border="0" align="middle" />
Short version:
Performance isn't good on an iPhone 4.
I had an animated sprite rotating 1 degree every tick. With each tap, I added one of these.
By the 15th sprite, the FPS started dropping. With 30 sprites, it ran about 10 FPS.
For action games it's unnaceptable, but for simple, turn/text games it should be fine. <img src="smileys/smiley9.gif" border="0" align="middle" />