Sony launched their music download service today -- "Connect".
The service, however, appears to be built around supporting Sony's own MiniDisc format, which has not seen significant commercial success over the past several years. Sony is expected to introduce high capacity MiniDisc devices later this year.
While songs are similarly priced to the rest of the industry ($.99/song), Sony will be using the ATRAC song format, making it incompatible with most MP3 players and the iPod.
Sony will be aggressively marketing the new service with cross promotion with United Airlines and McDonald's. Apple and McDonald's were originally partnered to promote iTunes in a cross-marketing deal, but this deal was reportedly changed at the last minute in favor of a Sony/McDonald's deal.