I've got to know the Shinogawa area relatively well as I've chosen to stay here (at nearby hotels rather than the Strings) on several occasions. Main reason is the ease of transport elsewhere rather than because of any love for the immediate vicinity.

I posted some maps earlier on in this thread - if you press on one and select the satellite view you can see how the high rises quickly become a downtown area full of modest residences a little to the South East.

One floor down from the hotel in the immediate vicinity - on the Konan side of the station - there are plenty of izakayas (drink and food bars) to catch people who work nearby (and of these there are a considerable number) on their way home. There are a handful of small restaurants too. We went to a place serving Korean food just after 11pm last night and felt all the better for it. But the place is more of a transitory area which people use to get from and to wherever they are going. There's more going on before 10pm as there are a wealth of shops and eateries to cater to them all and tempting them to dawdle and spend some time there - which works. Place has a buzz all of its own.

For non-izakaya based post 11pm nightlife, you'll need to go elsewhere. But there are plenty of options within a 2,000yen taxi ride away.

We're currently slumming it at the Sheraton Miyako and will be here for 3 nights. We'll return to the Strings for a longer stay afterwards. If you have any specific questions about Strings/the Shinagawa area I'll be delighted to help.