Okay, ya caught me being silly. In all seriousness, I tried the memory foam route for a seat on my FXST, and it didn't turn out so well... It didn't have enough body... The real story is...
I had a Danny Gray seat on the FXST which looked very nice, but didn't sit so good.... so, I pulled the cover, gutted the foam off the pan, and layered on the 2 1/2" thick memory foam from a mattress topper until I had enough on the pan, contoured it with a hot knife and an electric bread knife, and replaced the cover. Looked great, felt nice sitting still, but riding it was another story. Everytime I hit a bump, I was hitting the seat pan. So I started over by shearing what I had off the pan, and adding progressively more and more higher density foam to the bottom until I had enough body to it to be comfortable on the bumps. I ended up with around an inch of very compressed memory foam on top of some pretty stiff automotive reconstituted foam. (looks like the stuff that they use for carpet underlayment...) It's now pretty comfy, but the memory foam on the top is still very soft, and that allows the leather from the cover to migrate around a good bit and sometimes it will bunch up. It's okay, but if I hadn't run out of energy I would have done it differently.
I think what might work well is to layer the heavy and memory foams in 1" panels running sidways and vertically... (Imagine looking at the seat from the side and the stripes run vertically and from the top they run sideways to the bike. I think that might give you the comfort of the memory foam but still give you the support of the heavier bodied foam, with the added advantage of stripes across your butt that would probably be real good for circulation but not get stuffed up your crack, (which is the experience I had with the gel pads...)
BTW, I had the tempurpedic bed for a brief time, but couldn't get used to it... I felt like I was trapped and kept hurting my back trying to get out of it or move. My wife liked it, but she's a young thing and gets used to most anything pretty quick, so she got us a sleep number, and then put a memory foam pad on top of it, which pleased everybody... Which brings me to... yes there are big differences in the foams. The first mattress topper we got came from Cost-Co, and the replacement was from tempurpedic, and the difference in the way the foam acted was night and day. The tempurpedic was much better. More solid and quicker to react, and had more body to it... so If you going to do a seat, that's the stuff I would go after.
Anyway, that my serious two cents worth... [smiley=beerchug.gif]