Why you should love KDE SC
KDE is total flexible. You can nearly customize every aspect of the desktop, how you need it.
Klipper is a easy to use clipboard. You can switch between the things you have copied very fast. This tool is copy&paste at its best.
This tool is amazing. Just press 'ALT+F2' and you can do everything. You can launch your apps, switch between activities or start a conversation with an contact of your adressbook.
Activities are very useful. You can create an Activity for each "real life activity". Each Activity has its own virtual workspaces, plasmoids, wallpaper and startup apps. For example you can have an Activity "Work" with the apps you need at work and an Activity "at home" with the apps you love to use at home. Of course you can pause Activities, so they don't use ressources of your system.
There is no need to minimize your apps, so that you can interact with your desktop or plasmoids (widgets on your desktop). Just launch the plasma dashboard.
"One backend to rule them all". Akonadi stores your pim data (eg mail, calendar, contacts, ...) from different sources (eg Facebook, Google, ...). Your apps can use this data in different ways (plasmoids, mailclient,...). For me, it is very important that it syncs with Google Tasks!
You can use KDE on different form factors of devices. KDE gives you always a look and feel that fits the fom factor.
Thanks to Nepomuk, you do not search for something, you find it ;-). It stores ratings, tags and other things which you have linked to your files, mails, music and so on. So you can rate an music title with Dolphin and Amarok (music application) can youse this rating for automatic playlist generation.
Screenshot from my configuration