JonF, that was the concept I think I was trying to wrap my head around: The mass becomes energy (whatever that may mean...it's a convenient description for the conversion of "particles of matter" to "photons" and such) that radiates away, essentially "taking the gravity with it."
I found an article pointing out that the sun is losing 9.13e-14 of its mass per year. As I suspected, this is an incredibly small amount. If I wander through my calculations on the mass of the sun and thus this means it would lose 1% of its mass on the order of 10^11 years. Considering it's only on the order of 10^9 years old and will only last about 10^10 years total, it would seem that the sun is only going to lose about one-tenth of one percent of its mass over its regular lifetime. As I suspected, you'd never notice this with any sort of typical equipment.
Mass has a lot of energy and fusion certainly liberates a lot, but not much of that mass will get converted into energy in the process.
Rrhain
WWJD? JWRTFM!