Hi Alex,
Hopefully I am not telling you information that you already know...
Media Center has the capability to access and play your Last.FM "Your Recommended" plus "Your Loved" and other default categories, in addition to having the capability to request and play your user defined artists. After you subscribe to Last.FM open up Media Center and access Player > Play Last.FM Radio.
Here is a snapshot of Last.FM "Your Recommend" music being accessed by my Media Center:
http://i386.photobucket.com/albums/oo303/Supersnake_01/LastFM.pngKeep in mind that you must subscribe to Last.FM before you can do that. They charge a nominal fee of $3.00 per month. After you subscribe, go to the Last.FM web site and sign in to your account. Then look along the top of the window for your account name. To the right of your name will be a little drop down menu arrow. Use it to select Settings, when the Settings page opens click on the Application tab and instruct Last.FM to connect to Media Center. You only have to do that one time, Last.FM will remember it was done.=====================================================================================
However, if you are on the Last.FM website and click their web site links or buttons for "Your Recommended" (or any other category or Radio Station) Last.FM will not call your Media Center. The same limitation applies if you request some music via the Last.FM program
per se. Am referring to the program that you download and install from Last.FM. However, if you have the Last.FM program running while you play music through your Media Center (it doesn't have to be Last.FM music) then Media Center will scrobble to Last.FM which enables Last.FM to add your musical selections and tastes to your Last.FM profile.
Media Center will scrobble to Last.FM whenever you have the Last.FM program playing on your computer.
Personally I rarely go to the Last.FM web site to play their music and always use Media Center to communicate directly to Last.FM music - that way I get to watch the slide show of all the web pages and photos related to the artist and music that I am listening to via Media Center. Such is done if you listen to your Last.FM streams while in the Media Center Theater View.
Until the prior said limitation is rectified Media Center can call Last.FM but not vice-versa.
[EDIT] Added 01.10.11
Use any of the following to enable scrobbling to Last.fm :
Tools > Options > Services > Last.fm > [ ] Submit playback information to Last.fm (scrobble)
Player (menu item) > Playing Now (menu item) > Scrobble 'Listening To'
Right-click "Playing Now" in the left tree and select "Scrobble 'Listening To' "