I'm planning on replacing my BB with a ceramic FSA. I've thought about retro-fitting my bearings in my wheel hubs with ceramic bearings and changing the deralleur pulley wheels to FSA ceramics (eBay for less than $100). If it has bearings, why not try ceramic? If you believe any of the science behind it, supposedly the reduction in friction helps save a few watts (really, really few) just by changing out bearings. So if you're building one up and can spec ceramic, go for it. Just don't say it makes you faster.

I've heard of the benefits being more pronounced in the wheel hubs than the BB. Also, not a performance benefit, per se, but ceramic bearings are supposed to be more durable, somewhat justifying their price

In mine? Nah. I'm running standard SRAM GXP's in 3 of my 4 race bikes. The tri bike has FSA's stock mega exo. No ceramics anywhere. As I have a spare GXP sitting around the house, I may try to remove the bearing seals from it and replace the grease to see what sort of difference you can get just from that. I've heard about 95-98% of the performance of ceramics (minus the reliability...). We'll see if I ever find the time to do it. Maybe after cross season.

I'll assume you're not Armstrong and go with a 200W average over 56 mi, rather than 400... Making some general assumptions about crr (0.005), CdA (0.25), rider+bike weight (83 kg - we'll use me...), and standard temp/pressure, plus presuming no elevation change, popping the numbers into analytic cycling gives the following results:

200W (Standard Bearings): 22.64 mph = 2:28:25
204W (Full Ceramics): 22.82 mph = 2:27:14

0:01:11 is a none-too-shabby drop in time just from swapping to a ceramic bearing bb. But keep in mind this is the maximum difference you will see and will only be found with a non-sealed bearing set-up. If you go with a sealed ceramic option, you probably won't see any difference other than increased longevity.

If I run this again for an olympic split in an hour flat we see the following:

255.4W (Standard Bearings): 24.85 mph = 1:00:00
259.4W (Full Ceramics): 25.01 mph = 0:59:37

Yeah, I'll save 23 seconds, but to me that's not worth it. Instead of all the added maintenance coming from cleaning and re-greasing my bb every 3rd day, I could spend the extra hour or 2 per week training on my bike and be able to push 10W more on the course and save 50 sec instead.

Yes. The majority of the friction in any bearing set-up is caused by seal friction. Basically, the nylon seal that is installed to prevent grit from getting between the balls and races contacts the balls directly, as well. It is this contact that creates the drag. You can just as easily get the performance of ceramics out of a steel ball bearing by removing the seals and using a light oil lubricant. There is very, very little friction between the balls and races of any bearing.

The downside of using an open/shielded steel bearing is that grit will definitely get inside and foul the balls/races. The benefit of ceramics is not, per se, the decrease in friction, rather the increased hardness of the balls and races. Instead of being pocked by grit, ceramics instead pulverize it, thus increasing longevity. That is the real advantage of a ceramic bearing set-up. Just remember that you need ceramic balls and races for this to be the case. Only using ceramic balls will not give you much increased life span as the races will be damaged just as easily as in a steel balled bearing.