I reckon it will have no effect on the ps3 sales. Maybe a week boost at the most.

PS3 will drop the price on their console within a month just in time for the launch of GTA IV.
Anyway when do we get a Ninitendo Wii price cut? 16 months and no price cut yet on the Wii Nintendo Entertainment System.

Sony doesn't need to change anything

The bundle is already here (GT5pro, 26 march in europe) and even if the Xbox360 increases her sales, it will not dramatically afect the PS3 sales.
Someone that buy a 199euros Arcade is not able to buy a 400 euros 40gb.

And the Xbox360 is taken in sandwitch by the Wii and the PS3. PS3 takes the hardcroe while the Wii takes the casual. IF, this point not dramatically change after the price cut then the Xbox360 will be dead in PAL (which mean WW actually).

They won't do anything until GTA IV. They have no need to, this price drop will probably only make a difference in the UK. In Europe it seems as though they are already buying the PS3 at it's £300/400Euro price over the 360 which in Pro version is cheaper.

If they want a PS3, they'll get one.