Successful Surgery
I thought I'd throw my experiences in. I just opened up my 27" and installed my Samsung 840 Pro (which previously had been running in a USB 3 dock). Despite a couple hiccups, all went well and it was relatively painless.
Upon starting out, I discovered that the guitar picks I initially got were a bit thick for the task. I improvised with the edge of some plastic packaging, which was thin enough to get in, and after running it along for a while, the edge was loose enough to get the pick in, which properly separated the tape.
Despite the small size of the connectors, the two screen cables disconnect easily (and thankfully reconnect just as easily). Once the screen was free and clear, I got to work on the innards.
I loosened off the left speaker to access the hard drive caddy (you could probably access it directly, but one screw is pretty tough to get at). After extracting the drive and caddy, I realized that my 2.5" to 3.5" adapter bracket (which came with an old OCZ drive) was not going to work. For some reason the screw holes were tapped for typical 2.5" screws, not the ones that go with 3.5" drives, and thus couldn't take the screws from Apple's caddy. Even if they did fit, the adapter was only half-length, so would have been free on one end (perhaps not the end of the world, but not ideal either, I didn't want anything moving around should I ever have to transport my iMac).
After a bit of worrying over what to do (not wanting to test my luck and wait for a different bracket to arrive), I tried out some zip ties. They worked beautifully. I wrapped two around the width of the SSD, and it sit quite snugly up against one side of the caddy. I should have taken a picture of this, but was more concerned with closing up the patient and making sure everything worked.
After reassembling the speaker, I set about applying the tape. I ended up going with
this 3M 4926 tape kit from DigiKey. It's five 4" x 1/2" strips of the 4926 tape that R.OG suggested earlier. It was the cheapest and most readily available option in Canada. I ended up cutting it in half length-wise, since 1/2" was definitely wider than needed. I applied 5 strips (two on the left side, one on the right, two on the top), which seemed to be perfectly sufficient.
Once the tape was applied to the machine, I attached the LCD connectors, but didn't put the glass on, in order to do a power up test. After everything looked good, I pulled the second side of the adhesive backing off and attached the screen.
I intentionally didn't apply any tape on the bottom, heeding R.OG's warning about making it hard to re-open (I noticed that even the bottom strip on Apple's tape caused some problems), but that did result in the bottom edge of the glass being recessed just a bit from the metal. You can only notice it running your finger along the bottom, or looking right down along the glass from the top. I think my glass is offset to the right by perhaps 0.1mm, not even enough to see, just enough to feel slightly on the left edge.
I'm not sure what the best way to go about re-attaching the screen is. I did it with the machine standing up, but it might have been better on its back.
All in all, it went pretty well, and it's great not having any spinning disks or external enclosures to deal with. Dealing with the adhesive would be nice to avoid, but I think it's preferable to worrying about dust under the glass like previous generations.