Transferred everything but the CPU heatsink and the PSU over from the old Define R4. Not as flashy, not as silent, but able to be taken back and forth between home and school.
Case: It's VERY small. I wanted to have a computer I could easily take with me out of state, and I love the idea of having a competent computer that isn't much bigger than a console. It was between this and the Silverstone ML08, as the ML08 can fit their SFX-L stuff, as well as a 3.5" drive with an easy hack. I decided on this based on looks alone. The GPU support works a lot better than I expected it to, though I think there should be a third fan filter for the intake above the CPU. I bought some extra Silverstone ones and just moved everything outside of the case to make it easier to clean, as they're all magnetic.
PSU: To be honest, I actually bought the case with the included 450W PSU. From everything I've read, I believed it would be just enough to power the whole system. But for whatever reason, occasional power draw spikes from the GPU would freeze the display and overheat the card until the fans maxed out. Since getting the 600W gold-rated replacement, I've had no issues. It's nice that it comes with shorter cables, but there are four SATA power connectors and the extras get in the way, as well as an extra 8-pin PCI-e that I don't need since the Strix 970 only takes one. Cable management got real annoying real fast.
CPU: Originally bought to overclock inside the nice big Define R4, cooled by an NH-U14S. Now it's just a very decent quad-core running at stock speeds. I've actually since de-lidded it and replaced the TIM once with Coollaboratory Liquid Pro on the previous ATX motherboard. Couldn't be bothered to buy it again when swapping motherboards, so now it has Noctua NT-H1 stuck in there. No noticeable temperature difference.
CPU Cooler: It fits within the motherboard VRM heatsinks and the case ceiling. Not overclocking anymore, so that's fine. I really liked my old NH-U14S, so I went with Noctua again.
Memory: 8GB of 1600MHz memory is plenty for me. I removed the heatsinks for clearance reasons, and I think I like the new look better.
Storage: SSD for OS, programs, and samples. HDD for games and project archives. I have an external 3TB with all my movies and shows as well. A little disappointed that I couldn't fit a larger drive in there, as 2.5" only goes up to 2TB at the moment. Perhaps setting up a NAS will clear up the extra USB cable and power line required for the external drive.
GPU: Upgraded to a 970 from my previous 760 shortly before I decided to go mITX. My framerates in most games have doubled, and I absolutely love the current fan-off-when-idle trend. HOWEVER. The case obviously doesn't handle hot loads all that well, and the fans don't stay off for long, even when watching Netflix videos. I found out that standard 25mm-thick fans fit perfectly under the GPU, so I took out the GPU support bracket and put in two 120mm Noctua fans with nice rubber corners. The temperatures plummeted, and the two 120mm fans spinning constantly at 40% speed is still much quieter than having the GPU fans ramp up and down.
Regarding the infamous mITX cable management, I'd say that once you plan everything out, there aren't any spacing issues, but plugging stuff in and out and trying to get cable ties around stuff is difficult. The two extra SATA power plugs were an especially giant pain. The power supply was a very expensive oversight as well. But the build turned out well in the end, and I'm quite pleased with it now that it's done and over with.