In a nutshell the report says it's likely that the Jubilee Line upgrade won't be finished until October 2010 - making it more than nine months late. In the meantime a proposal has been made to split the work in to more manageable chunks.
London Reconnections goes into the report and what it might mean, far better than I could, so I'd suggest you read that.
In summary he concludes:
"Overall, therefore, the report is well worth a read - whilst it may need to be reworked and re-evaluated after Tube Lines impending takeover, it nonetheless still contains an interesting perspective on the current situation, and it throws an interesting light on the problems those upgrading the Jubilee Line will likely still face - be they Tube Lines or London Underground.
Whether we see a reduction in full weekend closures as a result of TfL's impending buyout of the company remains to be seen. If we do though, it seems likely that this will not be without cost - the temporary splitting of the line. Whilst that may be an improvement, it will still not be a pain-free experience."