All in all I'd say the project takes "much longer than a weekend" to complete, and is best done with the help of another person - if only just to move the several hundred pound bathtub from place to place. However, once done, you'll have a one of a kind piece of furniture that really speaks for itself. Having made it, instead of bought it, will really speak to your abilities as as a creator of things, and that's cool too if you're into that sort of thing.
Step 1: This Idea is Not New
There is currently a reproduced DIY version on a french blog, however it provides zero instruction, and takes a slightly different design approach by using an elevated seat. There's also a retailer on Etsy called Redux Tubs out of Canada who is selling the couch from $1,100 and up. Finally, my co-worker Carley has also wanted to build a bathtub couch for some time.
I think I am merely riding the groundswell of claw foot bathtub couch interest, as we all our - I simply have taken the time to document the process so that we may have the opportunity to make bathtub couches while hopefully learning a bit from my mistakes. I in no way take credit for this idea.
History accurate as of publish date September, 2012.