I would like to recommend a YouTube client to you. It can download and preview the videos on the Metro mode. Most of all, it is totally free.
YouTube Pro enables you to play YouTube videos in HQ and HD by 3G or WiFi and download videos to your phone for free.
1 Download YouTube videos (supports resume broken downloads)
2 Record and upload videos to YouTube (Resume broken uploads support)
3 Sync the downloaded videos with your PC by installing a client on your PC. (Link of the client and documentation: http://supertube.codeplex.com
4 Background downloads
5 Play the sound of the video under lock
6 Set channel to push notification
7 Playlist, Inbox, My Video
8 Choose and order the sections in the main page
9 Inbox push notification
10 Fast App Switching (FAS)
11 Subscriptions, favorites and search support
12 Map Tube: view the videos near your location
13 Comment in small screens while playing videos; Full screen in 16:9 or 4:3
14 Custom backgrounds
15 Local player enables you to play a custom playlist or play all videos
16 Video sharing via Facebook, Twitter, SMS and Email
17 Multi-Language and Multi-region support
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If you want to remove adverts, Please buy the paid version.
YouTube - Paid version
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Its price is 0.99 USD now. We will raise the price to 1.29 USD on March 31, 2012.
If you are interested, please try it.(If you can't find the app at the Marketplace, please wait a few hours. It is probably delayed in some countries.)
If you are a user of SuperTube, please don't be disappointed. It is delayed due to a bug. It will be updated to newest version in a few days. Its functions are the same as YouTube Pro's. If you would like to preview the new features, please try the free version of YouTube Pro.