I use a mixture of units:
- Long distances in miles, but I can usually work it out in km too (and chains if railways are involved)
- Short(ish) distances in metres (eg: 30m); I have no comprehension of yards!
- Very short distances in cm, mm, inches or feet depending on the circumstances, such as the equipment I'm using
- Weights in kg and grams, and tons (or is it tonnes? Whichever is 1000kg, not that it matters in speech, or simply writing 5T!)
- Volume in litres
- Speed in mph (preferably) for cars, metres per second for classroom use
- Pressure is Newtons per square metre in the classroom, psi in real life!
So it could be summed up as follows:
- Real life = a mixture
- Academia = virtually all metric
Notably, many items are sold in "metricised Imperial", such as jam jars (454g/1lb), fence panels (?m/6ft), wooden boards (8x4ft), and so on.
Also, fuel goes into the car in litres, which is fine. However, I can only comprehend (and compare!) economy in mpg!
Personally, I'm happy using a mixture of both. What annoys me is when people say things like "metric is soooooooo much better because you simply say 'it's about 1m' rather than 'about 3.281ft'" (and vice versa) because, in this example, you would say "about 3ft", rather than to 3dp.
Also, Imperial is good because cm is a bit small to be a good measure. For example, one foot (2 syllables) is quicker to say and easier to immediately comprehend (if you understand feet!) than thirty centimetres (6 syllables), so perhaps Imperial is safer as it can get the message across quicker?
Incedentally, one of my friends, who is predominantly metric, uses feet when directing reversing vehicles.
I'm 18, so was only ever taught metric at school.