The people who are interested in singstar and want to buy a console for it, will buy PS2 instead of PS3. So i don't think that singstar have effect on PS3 sales. And the PS2 Singstar does have country specific editions, which means that PS3 Singstar don't have benefit over the PS2 ones.
The 360 sales propably declines until Halo 3 release, then goes up, starts to decline again until december and after christmas it nearly stops selling for a couple of months. I would believe that PS3 sales are pretty much even with 360 sales for the rest of the year.
I don't think games like Mass Effect, Eternal Sonata or Blue Dragon have big effect on 360 sales, since people expect more games like Bioshock, Gears of War and Halo 3. Of course there are the certain group of people who like Blue Dragon etc. but it's smaller than the group who likes shooters, but this group usually plays with PC, so it's interesting to see that how much effect will it have.