I've been doing some more test ripping and noticed this in the Info Log:

"FLAC: Warning: Normalisation gain would have resulted in clipping, gain has been reduced to prevent this: Loudness=-17.78LUFS, Gain=-0.22dB, Maximum True Peak=-1.00LUFS, True Peak=0.00LUFS, New gain=-1.00dB [clDSP::EndConversion]"

What exactly does it mean and is it anything to worry about?

I have LUFS set to -18. I'd prefer to not set it lower as I'm concerned that this will make the playback on my iPod too quiet (I'm in the EU so my iPod is capped). OTOH, if the warning message is problematic, then I guess I may HAVE to change it....