iMac is possibly a bit more complex due to the big ass screen you have to remove.
But the biggest headache was really disconnecting and then re-connecting the cables attached from the motherboard to the back of the LCD. You can only lift the screen up a few inches because of those cables being quite short. So you have to creep your head and fingers inside this pretty small space to disconnect these delicate ass cables hoping not to lift the LCD too high and snap one. (look here for pics of teardown:
http://www.ifixit.com/Teardown/iMac-Intel-27-Inch-EMC-2309-and-2374-Teardown/1236/1)
Also, because I went the cheap way I had some difficulty mounting my SSD in the optical drive bay. I modified the existing bay to house my SSD so that took a bit of time. I chose not to buy one of those pre-made optical to SSD bays. Which lead me to my next issue...
The slimline SATA cable needed to plug into the optical bay slot. The optical bay SATA port is NOT a normal SATA port. This need is usually bypassed by buying one of those expensive optical to SSD bays. It has the adapter built right into it. But since I DIY'd the bay myself I had to find a Male Slimline to Female SATA cable. HELL!
Boot time is as you said about 5-7 seconds. Shutdown time is a bit slower. I'd say it's almost equal to or a bit slower than what it was on just the mechanical drive. I have theories on this but I haven't spent the time to look into it as of yet. I still have my mechanical drive in my iMac as a media drive so I'm thinking because I still have that drive in, plus the SSD, the iMac is taking just as long as before, if not longer, to shutdown, because it's shutting down both drives. Not sure though. My media drive doesn't have an OS on it.
I also upped from 4GB TO 8GB of ram. Figured why the hell not? Whole thing cost me just over $100 bucks. I only got the 64GB SSD and it is plenty.