Since these posts some more features were added to the game, so I thought you could use some new feedback.
First a small correction, addition to pablem's post:
Mining = 1xp * class/unit mined (can be done almost anywhere at whim) -> so 1xp/unit for class 1 ores, 5xp/unit for class 5, ...
Freight = 10% of payment (limited to supplies, if any, between x and y) -> 10% is for Dumont, higher percentages for Janisar and Dryden, also higher skill level gives higher payment and thus higher xp.
Trading = 6xp/unit traded (limited to supplies at source, requires up front payment)
Combat = fixed amount per kind of pirate, increases with pirate's level.
Salvage = 1xp/unit
Harvesting = 1xp/unit
Then a small feedback:
In my experience the xp system is nicely balanced, since I see my different toons gathering comparable amounts of xp.
The only thing that I find a bit out of balance is the xp for the salvaging.
Usually my combat toon does the combat in one browser and another toon does the salvaging in a second browser. However, the number of salvage units that can be taken is so low that hardly any xp is gathered. In the same amount of time any toon can earn a lot more xp with hauling, mining and day trading.
For example compare the yield (min:4/max:7) of a coyote salvage laser giving 1xp/unit, with the yield (min:15/max:18) of a ferox ice mining laser giving 7xp/unit.
My suggestion would be to raise xp for salvaging to something between 3 and 5xp per unit.