Dylan - trains are supposed to start running on the ELL on Sunday May 23rd - which is the same day the new timetable comes in. The new timetable creates the gaps between the Southern trains that allows the ELL trains to run - 8 trains an hour for most of the day. They should be running on the section north of New Cross Gate now but opening has been delayed - apparently there have been problems with the CCTV systems that allow drivers to see that doors are safely closed.
If the line doesn't open on May 23rd, there will be major problems on the evening of Monday May 24th because there are fewer services running to/from London Bridge in the new timetable - although still 6 trains per hour during the morning peak.
The Forest Hill Society is planning an outing to celebrate the opening of the line. Watch the Forest Hill Society Homepage for more information.