I have heard this a few times now (including from someone I met at lunch today), so I thought it might be worth clearing up a rumour circulating around parts of Forest Hill.
Forest Hill Station is NOT about to close for 2 years.
There was a poster at the station for a while (it is gone now I think) that seemed to imply that this might be the case, but it refers to the East London Line (ELL). The ELL will close from New Cross Gate to allow for the upgrade and building on that line, but the train services to London Bridge will not be affected.
"The line will continue to operate between Whitechapel and New Cross/ New Cross Gate until 22 December 2007. The line will then be closed to allow it to be converted in preparation for the new train service." [from the TfL website]
No need to panic!
If you want more clarification, check out the discussion thread on SE23.com.