Stephen Younge said:

I live in Boulder, CO, and my Early Girl Improved (planted in late May) is
huge and dripping with green tomatoes. However, as August approaches, the
plant seems to produce more and more green fruit, with no signs of any of
them ripening. Should I begin to prune flowers or leaves off of the plant to
focus its energies on ripening the fruit?

For plants that are loaded with green fruit, you can try root pruning.
From an earlier posting in rge:

Trick for ripening Tomatoes....
According the the book by Dick Raymond; The Love of Gardening,
you can make your tomatoes ripen faster if you do "root pruning"
when the tomatoes are green. Root pruning is where you take your
spade shovel and cut into the earth in a half circular pattern about
12 inches from the plant. Supposedly, this cuts into the root system
and triggers the plant to ripen the tomatoes. Try it!
Let me know if it works for you.

---pete---
-------------------
CORRECTION....
.....cut into the earth in a half circular pattern about
6 inches from the plant ( NOT 12 inches).

Supposedly, your tomatoes will ripen within one week.

[end of quoted materia]

That having been said, growing tomatoes on stakes (with regular pruning of
side shoots) will give you ripe tomatoes earlier than growing them unpruned
in cages. You get fewer tomatoes per plant this way. But you can plant more
plants in less space and, for me, that means more variety. Early Girl Improved
is well-suited to staking.
--
Pat in Plymouth MI

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)