In the UK, it's reasonably uncommon to find people wearing earphones in cafes. Most cafes have a good selection of music. It's more common, at least around here, that those working on laptops are students doing work. Often they will meet their friends and work together.
However, there are workers in these cafes too - and their etiquette is atrocious. I often see people leave their computers at the table, and head out to do some shopping in the local shops. Often they would have loud telephone conversations or conference calls. One even came back with their own food. When the cafe staff said "sorry, you cannot eat your own food here", they replied "oh, it's okay" as if the cafe were apologising!
When I bring my laptop, I make sure I spend the same amount of time in the cafe as if I was using it as in any other way, and never over the lunch period when tables are at a premium. One drink per hour seems fair.