i'm using such a setup. as u prob already know s2 doesn't support d-ttl or i-ttl. so u can use ttl mode or A mode.
under ttl mode, apparently it doesn't seem to work too well with anything above iso 400, ie, iso 800 and 1600. i believe this is stated in the s2 manual.
so most of the time, i'm using AA mode (it's like A mode except instead of comparing the aperture value on the flash and body, it compares it in terms of +- ev). example, if body at f5.6, and u want 1 stop brighter for flash, you would set to f8 on the flash in A mode, but for AA mode u just dial in +1EV. this works pretty good.