As mentioned with previously, an international transfer is < 24 hours. I found this "loophole" as cost effective in scheduling business meetings accross the US. A recent itinerary;

Tu - SFO to DEN - Depart 6:49 pm, Arrive 10:11 pm
We - DEN to DFW - Depart 6:30 pm, Arrive 9:30 pm
Th - DFW to ORD - Depart 7:15 pm, Arrive 9:38 pm
Fr - ORD to LHR - Depart 6:20 pm, Arrive 8:15 am (Saturday)
Su - LHR to IAD - Depart 4:30 pm, Arrive 7:30 pm
Mo - IAD to SFO - Depart 5:50 pm, Arrive 8:36 pm

The fare was priced as a SFO to London roundtrip (approximately $650). This was much less expensive then pricing individual, point to point fares. The other benefit, is that I was able to upgrade these flights using 2 United SWU's.

A couple of weeks ago, I booked an award ticket for an upcoming trip.

Mo - SFO to LAX
Tu - LAX to OKC
We - OKC to PHL
Th - PHL to IAD
Fr - IAD to LHR
Tu - LHR to SFO

It was not easy booking this award, as there appears to be additional restrictions (versus paid ticket). After several calls with the award center (and various explanations on why this routing is not permittable), an agent did ticket this itinerary.

The one major catch was the mileage limitation on an award ticket.

HChrist, you may be able to spend 2 days with your friends (coming and going) by transferring via their city.