Like Keef, I too enabled the boot scan but have now disabled it as it is very slow - but thorough.
On balance I think AVG 7.5 was the best I have seen and I would PREFER now to return to AVG 8 - if only I could find this darnned 'another anti-virus/security programme' which is stopping re-install
Getting some assistance from the AVG forum at the moment, so will report further. In the meantime I have uninstalled Avast and am trying Avira free which seems to have better options.