[mgbmtl]

That still seems rather high to me. I usually aim at having 3-4 billable hours per day. The rest of the time, if I'm not slacking off, I put into improving the product or sales.

Even for salaried workers, I don't think anyone would expect them to do actual productive work for more than 3-4h of programming per day (rest of the time being spent on meetings, planning, office distractions, etc).

[hnick]

Even in an office environment I've seen rough estimates of 5 (6 at most) 'billable' hours per day for longer term projects. The rest is admin, housekeeping, chitchat, etc.

Studies seem to support the 4-5 hours of useful work per day over long periods. It's easy to peak at 8+ for a short time (and twice as easy for personal passion projects) but it wears off.