Download: Android Market v3.1.3 (mirror) (for all devices - does not require root, but you do need to enable 'Unknown Sources' in the Settings-> Applications menu.)
The Market update in this post is meant for phones only - there is no known update to the Honeycomb tablet Market at the moment.

Wow, Google is on a roll with the Android Market lately. Since the release of Market v3.0, a number of small updates have come to the Android Market recently, but this is by far the biggest yet. Google has added the long-awaited +1 functionality to the Android Market (which has been on the web version of the Market for quite some time), along with a few other goodies.

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There's a brand-new settings menu, as well as click-to-read explanations of app permissions (not developer customizable, unfortunately).

There are also 2 brand-new Market icons to spruce things up a bit (within the Market itself - unfortunately, the app drawer icon is still the same).

For convenience's sake, the size in megabytes of each app, along with its latest update date, have been moved from the bottom of descriptions to the top of individual app pages, which is a very useful change in our book.

Moving on to the thumbnail navigator, Google added a long-overdue sliding transition - a nice touch that makes the Market feel more polished.

Oh, and did we mention you can now use an optional custom PIN for purchases on your phone, instead of leaving your Google Checkout wide open for anyone that picks up your device? If you have kids, or your phone is stolen, this is one awesome feature to have - and really, it makes a lot of sense.

You can get the new Market .apk here (mirror), root access is not required, but you'll need Unknown Sources enabled in the Settings -> Applications menu to install it.

Thanks, Patrick! (@Tiemsch)