+1 Krita user.
Not really… Krita is more like an open source version of photoshop that uses all the new KDE4 and Koffice technologies. It’s the photomanipulation / painting part of the Koffice suite. The Koffice suite, however is a freedom oriented, open source office suite. It has many more parts than MS office though (project management, vector drawing like Illustrator, painting in Krita etc).
Anyway, if you like MS office, give Koffice a try. If you like Illustrator, give Karbon (part of Koffice) a try. If you like Photoshop, give Krita (part of Koffice) a try.