re: OT Mechnics- Running an car without an air filter. How bad is it for an car?

You can run an oil analysis from a company like Blackstone and quantify the damage, unless you changed the oil already. Great way to put a vendor in a corner when they make a idiotic mistake like that- there is not really an excuse to forget to put a air filter in, but remember to clamp the filter housing back down. Most vehicles have a tight seal and it takes some doing to get everything lined up when the filter is present.

Even better is the MAF sensor probably has a nice layer of dust on the element and inner workings now- the very sensitive element and inner workings.