This week I had the privilege of ordering and installing a new iMac for one of my customers. Financially I had some doubts about the new fusion-drive, but it turned out great. The thing is super-fast. Writing files is a matter of seconds and starting the most used apps also. In my opinion fusion-drive does what it promises.
Overall the machine looks great, feels great and is really an icon on the desktop. One thing that might be bothering in the future is the inability to upgrade the memory. The 27 inch has a memory slot that you can open, but the 21,5 inch has not. The machine comes with 8GB of RAM, which is in my opinion more than enough for the foreseeing future.