I have no sympathy for this troubled young lady's bad behavior, which has endangered the public, but as I commented Thursday in a discussion thread with Anne at Just Muttering, the underreported story is that what's unusual about Hilton's treatment is not that she was freed to serve at home -- it's that she's serving any time at all, in a jail where a 90-day sentence typically means anywhere from hours to a day or two served, and sentences over 90 days are served at rates as low as 10 percent, which is often far less than even her reduced sentence of 23 days.
Some links I rounded up on the state of the California penal system, particularly the L.A. County jail, can be found in the discussion at Just Muttering.
The judge is attempting to make Paris an example, and she's also being used as a pawn in a power struggle between the judge and the county sheriff.
Based on the cases I've been exposed to via my legal proofreading business, my understanding is that once a defendant is sentenced to county jail, it's usually out of the judge's hands and a matter for the sheriff. Judges regularly sentence defendants to county jail with the realization that their sentence will, in all likelihood, not be carried out.
To their credit, the New York Times and the L.A. Times pick up on this angle today, but the media in general have not done an adequate job covering this story, with many instead portraying her "special treatment" as getting out early.
June 13th update: More from the L.A. Times, which conducted a study verifying that Hilton is doing more time than a majority of inmates sent to the L.A. County Jail.