I do if it's equipped with one. On my AR I train to disengage it when I bring it onto target, and disengage when I got back to the low ready. It even goes on for reloads. It's sometimes a PITA, but it's there and as such I believe it needs to be addressed. A slung AR also presents a host of additional concerns for a snagged trigger (especially in tactical gear with a bunch of crap hanging off your chest) compared to a safely holstered handgun. I also try to maintain positive control of the rifle with at least one hand whenever possible, because I still don't like to be wholly dependent upon that safety lever alone to prevent an ND.Do you use safety's on a rifle?
I don't have a problem with a manual safety on a handgun, but it does simplify the manual of arms not to have one (which can be vital under stress), and if someone does elect to carry a gun with one they need to train to use it.