I picked up a Mac Mini 2012 i5 2.5Ghz on the Apple refurbished site for £339 on the weekend, it's due to be delivered tomorrow. I currently use my Macbook Pro 2009 2.26 GHz Core 2 Duo as my main machine, it doesn't leave the house anymore and have it hooked up to a 27" 2560x1440 panel. The onboard graphics really struggle with the resolution of the monitor in terms of smoothness, Yosemite transparencies and redraws but I do have an SSD and 8GB RAM which I will switch over to the Mac Mini when I get it and perhaps look out for 16GB RAM for the Mini and put the 8GB back in the MBP and delegate it as a dedicated portable computer.
I'm a bit anxious whether I should have waited for the 2.3Ghz i7 which goes for £479 on the refurb store, it may never show up and the Mac Mini which I did manage to order ran out of stock pretty fast (<2 minutes, limited supplies naturally). To be honest, although I view myself as proficient, and a power user, my needs aren't actually that high. Most of what I do revolves around the browser, with a few miscellaneous apps which don't really need that much power. Occasionally I use Photoshop as I do some web design/general design work now and again and I do use Lightroom semi-regularly. But in terms of future proofing the computer as I'd like to use it for a considerable time and the i7 seems to provide considerable clout over i5, of course the latter being a capable chip indeed. On the other hand, with 16GB RAM and an SSD (perhaps 2xSSDs in RAID 0, very likely overkill), the i5 Mini is a solid little machine. Realistically, I'd like it to tide me over for two years till I think about 5k screens and such.