Sony makes really great hardware, and (most of the time) utterly wretched software. Sony could be a much better company with Apple's help. Not sure how such a merger helps Apple, though.
Sony manufactures TVs and other electronics. Apple could bring this in house rather than having the likes of Samsung and Foxconn manufacture their hardware. There is also Sony Pictures Entertainment, Sony Music Entertainment, and Sony Computer Entertainment.
I rather doubt the rumours though. There would be many business units that would have to be spun out or shut down. (Sony Ericsson, Sony eReaders, BluRay, etc)
I like Sony. I like Apple. I'd like to see Sony find its way again and start competing hard and innovating.
Apple also makes really great hardware, and (most of the time) utterly wretched software- see itunes, iphoto, etc....
Not sure how this would help either company. Apple doesn't need any help getting really great hardware made. If anything, Sony would bring the quality down considerably.
Such a merger will never happen and if it does it will be a dangerous move for both. People never think about cultural match when discussing mergers.