I'm a computer guy for many of my friends/family. Besides cleaning system from bad, bad and nasty things , installing better software and educating why to use it, this also includes promoting of useful services that exists on the web. Many times I am disappointed to find out that most of my friends now a little about them. A lot of people use computer only for Web surfing, email poking and music playback. This has inspired me to write down the list of services I use and might be generally useful to others as well.
Most of them use principles of Web2.0 (which in short is about socializing the web using latest technologies to provide dynamic rich content/services). There is a lot of Web2.0 services around, from famous google maps, picture sharing at flickr to massive tagging systems like delicious or digg.
Today I introduce last.fm, at first it looks like web radio station. Type the name of artist and it plays it for you. Behind is much more, this site falls into social bookmarking category. Users listen to the music just like they did, information about what they listen is send to the service and stored in the user's profile. When listening to music every other day (like I do) during few months there is enough data about user's taste so the system is able to recommend new never tried artist or someone who shares the same music enthusiasm. From already played songs that are free to broadcast over the internet system creates radio. So when next time someone asks "What are you listening to?", just give him your last.fm profile.
What I do like about this service is that it is non obtrusive. Just listen to your music, statistics are generated automatically. Also I found it great site for checking for background info of who you listen to. For example you get some music from your friend, throw it on your last.fm enabled player (i.e Rhythmbox or Muine on linux), play it and if you like it, open your profile (mine in this case) on last.fm and click on the name of recently played artist. Many times a lot of information about the band is revealed including similar artists that may interest you as well.
There are also many other additional features provided by this site like joining groups, chatting with friends and blogging about recent music actions, even those are rarely used (at least by me) you can use them anytime later.