Covers all the request features. However since the move to akonadi it does have a terrible reputation for bugginess, unrelalibility and resource hogging, unfortunately a not undeserved one.
However it has been improving steadly, even drastically since kde 4.7. I've been using it as my primary even despite the problems because when its working :) it is just so good. Fantastic integration with KDE, really good handling of multiple accounts and identities. PGP & SMIME, integration with Google calendar and contact, as well as other 3rd parties. An open plugin system for extending it. And it looks *really* good, the perfect blend of functionality and sexiness - when its working :)
I just upgraded to KDE 4.10 Beta 1 (via Kubuntu raring). There seems to be another qualitive improvement in reliabilty. Akonadi hogging the CPU seems to be fixed. Message searches are working - full text content and attributes.
There's still progress to be made, but its made huge steps and I finally feel confident in saying Kontact is back and will make it. The developers have the feature sets done and are just focusing on bug fixing now.