Ice vs heat treatment

So, after a soft tissue injury, do you ice or apply heat?

The answer is pretty clear for acute injuries - it's ice. Ice may not help but it doesn't seem to hurt. Which is consistent with the old acronym I learned in junior high gym class (one of three things I learned that semester, along with the fact that I was fat and I hated running): RICE for after a sprain:
R - rest
I - ice
C - compression
E - elevation

The idea behind ice is to slow metabolism and reduce the need for energy and oxygen delivery, which after injury is hampered by damage to vessels and surrounding tissue. This in turn reduces inflammation and swelling. However, there are few prospective studies in humans, and in reality strains and sprains almost always get treated with ice as well as compression.

When to switch to warmth treatment, on the other hand, seems less agreed upon. I've seen people say that it's acceptable to treat a "chronic" or nonacute injury older than 7 days with warmth, but it's very anecdotal. The general idea is to treat non-inflamed tissues with warmth - muscle spasm, "tight" joints, etc.