If you define "running ~well" as running at the same speed as it ran on the original PS1 hardware, then none.

However, please remember that this release is not utilizing the 3D graphics acceleration of the N900 yet, so to see the speeds that we are with some titles (mostly older PS1 titles) is VERY encouraging.

In it's current form, I've gotten speeds that make the following games playable on the N900 (note that my definition of playable may vary from yours):

Tekken2
Warhawk
X-Com: UFO Defense
Pepsiman (mega props that this works since I haven't had a working Japanese PS1 to play it on for YEARS....)
Dragon Ball Z: Legends
007 Racing

Please note that not only do the games run slower without GPU support, but it also taxes the CPU much more which really kills your battery life. I went through about 75% of my charge just in the first level of Warhawk.

Basically this is a proof of concept and a work in progress. Feel free to play around with it now if you dare, but keep your expectations in line and we'll all keep our fingers crossed for the OpenGL ES 2 support in the future.