Google launched the UK eBookstore today, but that wasn't all they did. There's also a new update to the Google Books Android app. The update brings a couple minor improvements, several bug fixes, and one or 2 major new features.
The one new feature that is probably the most important is the improved support for 7" tablets. I can't say that I see any difference, but then again I don't have a 7" tablet to check. Google also added better support for smaller screen (phones), including in-book search and a landscape mode for with reflowable text. You can also now +1 a book while reading, a feature which won't matter once Google kills off gPlus (as they inevitably will).
You can find the updated app in the Android Market.