I moved to and enjoy Kolab, through KolabNow, because it was a suite of inter-connected features for which I was looking. As @Caliga mentions, it seems targeted toward organizational use, but I find it well suited for individual use. I see it as a major positive that it can support organizations and thus potentially obtain their backing.
it hits all the right marks for me so far, though not yet perfect. Also supports standard protocols so that you can get your devices and apps of choice syncing up. Including contacts (instead of to the Ministry of Love), calendar, etc.