Fast? Who wrote n900 is fast?
In some situations yes, but extrem lag frequently occurs.

My n900 broke (micro usb port) now while it is being fixed (on warranty thank god), I bought an xperia x10mini pro.

What pros does the x10mini have?

Better apps for daily use
Better function as an usb modem
Better kayboard (how did Nokia **** this up? the n900 is 500times bigger and has a worse keyboard?!?)
It's a phone, not a crappy internet tablet with crapy phone function included

I may sell my phone when I get it back, but it would have to be to a hacker, cause I wouldn't sell it to a regular person. I would feel I was cheating them