Personally I do often.
Games I played 100% on a PS2 (never on a PSone) include Final Fantasy Tactics, Valkyrie Profile, Xenogears and Star Ocean 2.
Plus have replayed FF7, FF8, FF9, Resident Evil 2 and 3.

But actually I am considering not sending the PS2 to the 'bunker' alongside my Atari, Nes, SuperNes and Playstation... because the Siaxaxis controller won't have the rumble for the PS2 games...
So I guess... emulation or chip isn't really necessary.
Will just have to make space to fit the PS2, PS2 and Wii under the same television set...