A lot of people have been waiting for a very long time for their greencards due to backlogs in employment-based immigrant visas. USCIS recently published Questions & Answers: Pending Employment-Based Form I-485 Inventory regarding this issue and also published its current (as of August 25, 2009) inventory of pending employment-based I-485's.
There are a lot of things we still don't know. For example, we still don't know how many visa numbers are allocated to each preference category each month. However this inventory information is at least more information than we had previously.