Andrew Gierth's numeric abbreviated keys patch was committed recently. This commit added abbreviation/sortsupport for the numeric type (the PostgreSQL type which allows practically arbitrary precision, typically recommended for representing monetary values).
The encoding scheme that Andrew came up with is rather clever - it has an excellent tendency to concentrate entropy from the original values into the generated abbreviated keys in real world cases. As far as accelerating sorts goes, numeric abbreviation is at least as effective as the original text abbreviation scheme. I easily saw improvements of 6x-7x with representative queries that did not spill to disk (i.e. that used quicksort). In essence, the patch makes sorting numeric values almost as cheap as sorting simple integers, since that is often all that is actually required during sorting proper (the abbreviated keys compare as integers, except that the comparison is inverted to comport with how abbreviation builds abbreviated values from numerics as tuples are copied into local memory ahead of sorting - see the patch for exact details).