I used to agonize over how frequently to replace a chain, but Sheldon has reduced it to an exact science: every few months, measure the length of 24 half-links, and replace the chain if that length exceeds 12-1/16 inches. This practice will definitely reduce the wear rate of your cogs and chainrings. 2000mi or 3000km sounds about right to me, but "your mileage may differ."

Note also that microdrive systems wear out much faster than full-size or road systems -- chain tension is greater, and fewer teeth are bearing the load. Unless you race, avoid 11 or 12T cogs entirely. Avoid cross-chaining, and try to use more than just the same few gear combinations. (I save my lowest gears only in desperation, cruise at high cadence / light tension in my highest gears, and therefore tend to wear out my medium and low-medium cogs first.)