[ugh]

The iPhone’s PDF viewer is pretty crappy, though. It’s pretty much the only thing on the iPhone that feels unbearably slow. I don’t know how much the iPad improves that but at least on the iPhone reading (long, i.e. ten or more pages) PDFs is no joy.

[samps]

I have experienced the same frustration on my iPhone 3G. I can vouch that the speed is greatly improved on the iPad. The PDF viewer is now actually pleasant. (It's amazing what a little clock speed will do.)

[jacoblyles]

The iPhone PDF reading experience is actually better than many 6 or 9 inch eInk devices.

[tzs]

Try GoodReader.