I am pretty good with metric units because in the job I had before my DC were born I was constantly needing to make conversions between short, long and metric tons. I had all the conversion figures at my finger tips. So much so when DS was born and they gave me his weight in imperial and metric units, I knew immediately that one of the figures was wrong. So, there I was my first child just born and in my arms after a long and exhausting labour and all I could think about was the mistake in the conversion and wishing I had my slide rule with me as I felt too tired to work it out in my head.
Having said all that, I still prefer to work in imperial units. For me imperial units have an immediate tangible weight, length or volume, while metric measurements are purely of the mind and just do not have a 'feel' to them.