I’ve used Kontact or it’s email client component, Kmail, as my main mail client since, I think, 2005.
That was until I upgraded my main laptop to 11.10 with KDE 4.7 (and Kmail2). I tried, but I just couldn’t get it to work (I know it worked for some, just not for me). In Kubuntu we even tracked kdepim (the KDE component where Kmail lives) updates and when 11.10 was released it was at a post-4.7.2 snapshot when the rest of the KDE SC was still 4.7.1.
It wasn’t enough for me. I was stuck in Thunderbird (which is not a bad mail client, just not the one for me) until last week when KDE SC 4.7.3 and Soprano 2.7.2 made it into oneiric-proposed for testing and I upgraded that same laptop. It still took a bit of fiddling to get everything working, but it’s usable for me now.
These same updates were copied to oneiric-updates in the last day, so they are available for everyone now.