Metrotube, a popular third party client app for YouTube, has been updated to version 3.3, adding support for YouTube's "Watch Later" feature, which allows you to mark videos of interest for later playback. This list of videos is synchronised between the app, desktop website and mobile website. The update also includes a number of bug fixes and performance improvements. 

Metrotube's developers, Lazyworm Applications, has also announced that the app has been downloaded 100,000 times, an impressive figure when you consider there's not only an official YouTube app, but multiple third party YouTube apps too.

Metrotube has something of a mixed history. The original version, called LazyTube in its early days, was withdrawn from the Marketplace (just after we reviewed the app), but was later able to make a come back as Metrotube, as we noted in a story earlier this year:

Lazyworm Apps have announced that their popular YouTube client, MetroTube, will be returning to the Windows Marketplace for the first time in seven months. Withdrawn due to the lack of availability of a public API to access high quality video, the team have decided to bring it back to Windows Phone users as a free application.

Marketplace description:

YouTube. Beautifully designed. The #1 TOP rated YouTube app on the marketplace!

Metrotube can be downloaded from the Windows Phone Marketplace for free.

As noted above there's quite a few YouTube apps available for Windows Phone. Tube Pro is on of these, and it was also updated yesterday, to version 2.5, adding support for "Watcher Later", offline play-list support, Oauth 2.0 for log-ins, and the ability to change video quality during playback. Another option would be PrimeTube, which we wrote about here.