I've never had a memory foam, but I don't personally like sleeping on them because I enjoy rolling around during the night and changing positions, and I found the memory foam wasn't very great for this.

We have a bed with a Tempur-Pedic mattress on it, I'm not exactly sure how long it's lifespan will be since we still have it but I have also used other Tempur-like foam cushions and their life seems to be directly linked to the amount of weight and time used. If your significant weight and sleeping long hours I suspect the mattress will breakdown faster, the 'bounce back' time will be longer and firmness will soon be softened.
I have slept on the bed we have and while is does support your body it makes moving turning on side, or even getting up out of the bed after sleeping a bit more demanding. I don't care for that I like a firm mattress. Something they don't tell you is if you have a significant other and you tend to sleep close together often you both create a valley that you'll both sleep in, unless you keep some space between you it won't keep your bodies separate. Good luck you might want to try a place that offers a 60day home trial

I have a memory foam mattress I got at Wal Mart like 4 years ago. Its really firm and I like it a lot, but my girlfriend thinks its really uncomfortable because she likes a softer mattress

We have a Simmons brand memory foam mattress with a 2-3" pillowtop layer. It's actually a bit firmer than it sounds. We've had it about 4 years now and the best I can say is this; whenever we go away for an extended period of time, the one thing we miss the most is our bed. I wouldn't trade it for anything short of my children's lives. My back just feels so much better after sleeping on it compared to a spring mattress.

They do retain heat though. So if you sweat a lot, that might be a problem. I think my wife considers the heat retention a perk though as she's always cold.

We have had a Tempur-Pedic mattress going on 8 years I believe and my wife and I LOVE it! It does take some getting used to it, took us about a month, but I have had almost no back pain since getting one and I used to have back issues.

Certain ***cough*** recreational activities ***wink-wink*** also are a bit different with this type of mattress and my wife would NEVER go back to a regular mattress.

It was in the news that sex on a memory foam mattress was different, where people had the "bounce" of springs before, they don't with memory foam and had to actively work to find a better way of doing it. A lot of people were unsatisfied with that, while the sleep was good, the "fun" was more effort because the body sinks into the mattress rather than supported like it traditionally would be.

We absolutely love ours. We have a Serta iComfort and like the above person said, it's the one thing we miss most while away from home. There is nothing like coming home after a few days and laying in your bed.

The heat thing is also very true, as well as Mad39er's point. If you're used to the bed doing some of the work for you you'll be dissapointed when theres no bounce to the bed.