WARNING!!! - Thread Drift...
I know all of the above has concerned VFR flight, and I know how useless most liquid filled compasses are, but WRT to IFR, other than the compass how can you re-align the DG in flight? And how picky is ATC with regard to your heading accuracy? I can understand getting a compass checked every 24 months for IFR, but as Mach E says, in the bumps you'd be lucky to get any better than 15 degree accuracy.