"Has anyone had good experiences with microphones on Linux"

I've not had any issues with external mics and usb interfaces. Onboard mics aren't really that good to begin with; you'll want to get some sort of external lavalier mic, or a condenser or cardioid dynamic. Onboard mics and other omnidirectional mics aren't great because they pick up sounds from all over. A cardioid polar pattern helps a lot with cutting down on sound.