Has anyone had any experience using IPE on their boat?
Yes. I just used it this past summer Rich. It's known to me as Trex. Years ago when I lost my mast, I had a new Z-Spar mast set up with a stainless steel mast hinge by Kenyon. I told the rigger that I didn't want that el cheapo cast Aluminum tabernacle that came with my old mast. It had a built in sheave at the bottom of it for my Jib Halyard and I hated that set up with a passion. My mast would be an inch lower with the new mast hinge and the rigger told me that my upper stays were still good and he was going to use them and replace the lower stays. The difference in height was about 1-1/8" and I had to make it up by adding a piece of Teak under my new Kenyon hinge and the utility plate that I bought to go with it.
Through the years though, I would get get a tiny leak around one of the bolts that hold my tabernacle so this year I decided to replace the 12"X 5.5" X 1" thick Teak block with a piece of Trex that one of my friends gave me.
When our son Mike built our farmer's porch years ago, he used Trex for the flooring and I've had a piece of this stuff on my wood pile that looks as good as it did when it was new. Nothing can kill that stuff.
Anyway, when I had that rigger in RI work on my new mast, he built a mast plug out of stainless steel and through the years electrolysis set up between the two metals and it corroded the bottom of my mast so bad that I had to cut 2" off it. I brought my mast down to a big marine metal fabrication shop on the river this past summer and he told me that they would need to cut 2" off the bottom of my mast and piece in a mast and weld plates around it. He quoted me a price of $300 just for labor.

So I brought my boat home and had my son cut the 2" off the bottom of my mast and I sat down and did a lot of thinking past what I was going to use to make up the two inches and then it came to me. I'll use two pieces of 1" Trex in between the mast plug and the tabernacle hinge plate. Well it worked! I was able to sail my boat for the rest of the season with it. I had also ran the idea by Rudy of D&R Marine when I was in his shop one day this past summer and he said it would work with no problem. To make a short story long though, the Trex I installed under the tabernacle is permanent. I used Butyl Tape to bed it and counter-sunk the holes a little in the Trex and the cabin top, so I think it's going to work out a lot better than the Teak I had under the Tabernacle. As for the Trex in between the mast plug and the top hinge, it adds too much weight to the bottom of my mast and it looks kind of "hacky".
So in short, the stuff is great but it's kind of heavy unless you can buy thinner boards.
Oh by the way; I just drove by that large metal fabrication shop on the river yesterday and they're closed for good. I heard that they went belly up this past summer.
Joe