I did the migration this weekend, but hit a couple of snags.
First, the H100 is DOA. The lights on the pump will not come on, and the fans will not turn when plugged in to the controller (they will when plugged into the mobo fan headers, but holy crap maximum rpm is loud and I cannot seem to slow them down). The pump is making a really loud ticking noise and it gets louder every few seconds, have been scared to leave it on for more than 30 seconds.
Second, the 4 pin mobo power connector on my modular PSU, as others have said, is too short to reach up to the top corner to wire it under the backplate. I have it snaked under the GPU and up the backside where it just barely reaches. Is there anywhere I can buy replacement cables/extensions for my modular OCZ PSU? How have other people dealt with the short 4 pin cable?
Another snag was the PCIE/GPU power cables. Too short to reach the top PCIE slot (when passed under the backplate), so I seated the card in the lower one slot, which I believe is only 8x. IIRC the performance hit is minimal (like 1-3%), but that is also preferable because the top slot is so close to the CPU and memory that it creates a heat well. Spacing them apart puts the GPU directlyi nline with the top front intake fan, which is unblocked because I pulled the top HD cage out.
I will post pictures when I get the machine up and running again.
In summary though I would say these things:
The 550D is BIG. Its a mid tower on steroids.
The 550D is a fanastic case with good airflow even in default mode w/ all silencing material.
As others have said, Corsair does an excellent job with installation design and documentation. If they wanted to go above and beyond, they could give installation suggestions for common annoyances, but for the most part, the case is idiot and hassle proof.
One exception would be trying to install the radiator & fans after the mobo. It is really tight and I wish I had done the rad first. I suspect that to be the case with most mobos, though the fan headers on the edge of my board are a complete PITA to get to with those rad fans installed.
Last, and probably best advice - do not install a mATX board in this case unless you want headaches. Most of my problems are due to a cramped board form factor and a modular PSU w/ short cables/cables with excess, unneeded leads.