I have definitely used Imperial brass, and pretty well everything else too - Dominion, Remington, R-P, Peters, Rem-UMC, WW, WW Super, Super-X, Super-Speed, Norma, PMC, Lapua, IVI, DA, LC, goodness knows what else...
And I have had little challenges along the way with pretty near everything - but who knows if it was the brass, or ME? Or my gun?? or what???
I have become something of a snob in some cartridges, for example I pretty well only use Norma brass in .308 Win because Dizzy Dan has such great prices on it. I got some new Lapua in .243 from hithere and it is LOVELY stuff to work with. Where I notice a difference is when I am loading a given cartridge and change brass for whatever reason. All of a sudden, the brass is harder or easier to work with, depending on the change.
Bottom line, I would use Imperial brass if I had to, but it would not be my first choice. I think 'Boo's point about annealing is a good one, I have gotten away from annealing brass in the past twenty years or so, getting fat and lazy in middle age.......
Rembo I just might have some .243 brass here for you if we make that other deal we have been talking about. It is only fitting that some good brass follow that rifle west........
Doug