Yes well the SE X10 mini is very small compared to most other Android devices currently available. So you have trouble selecting the little buttons. Does it have a capacitive or resistive touchscreen? If the latter is the case, you could use your finger nails.
Also, the CPU in such a small device is not very fast which is why the app does not react sometimes...
I have a SE X10 mini, with android 2.1, I installed run.gps apk for that version, to see how my new phone handle run.gps.
The main problem i found, is that touching the buttons in the bottom bar, never worked at first touch... i have to try and try and try to make it work... also is there a small red pixel that goes around as we touch the screen, so I think there is some problem in run.gps in the input system.
All other apps work fine i tryed worked fine
Also the size of the icons in that bottom bar is ok, with my old mobile, that had a stylus pen! now that the touch is made with the thumbs is also harder to hit the right icon, propably you should do something in next vesion
By the way, when should we expect the next version, not for stylus pens devices :) ?