We often get questions around Microsoft Project Specifications and limits.  This helpful information was provided by MSFT. Thanks.
Enjoy,
Jacques

The following specifications are supported when you run Microsoft Office Project 2007 or Microsoft Project 2010 on Microsoft Windows XP Service Pack 2, Windows Vista, or Windows 7, although actual limits and performance speed depend on your computer's configuration.

Note   Out-of-memory errors may occur before you reach the listed limits.

Attribute Maximum
Resources per project 700,000
Resource units per assignment 60,000,000 units or 6,000,000,000%
Resource availability dates 100
Tasks per project 400,000
Task dependencies per project No limit
Predecessors per task 50,000
Successors per task 50,000
Outline levels per project 65,535
Consolidated projects 998
Open project files per consolidated project 998
Sharer files connected to a single resource pool

997

(That is, the maximum number of open project files, minus 1 for the resource pool itself.)

Open windows 50
Base calendars Tested to 30,000+
Calendar exceptions per calendar Testing was able to add more than 15,000 exceptions to a base calendar.
Rate tables to support varying pay scales and rates 5 per resource
Variable rates per rate table to support rate increases and decreases 25
Cost value in a currency field 999,999,999,999.99
Work value 1,666,666,666 hours
Assignment work values for work assignments 999,999,999 hours
Assignment work values for variable material assignments 999,999,999 units
Assignment work values for fixed material assignments 60,000,000 units
Custom cell formats 64,000
Print scaling adjustment range percentage 10%-500%
Page header text 5 lines
Page footer text 3 lines
Page legend text 3 lines
Page legend text box width 5 inches (12.7 centimeters)
Filter tests per filter 40
Filter tests per AutoFilter 2 per column
Earliest date allowed for calculation January 1, 1984
Latest date allowed for calculation December 31, 2049
Discontinuous selections in a sheet view 10
Baselines 11
Characters in a text field 255
Characters in an outline code field 255
Values and characters in an Enterprise Resource Multi-Value (ERMV) field 255 values, each of 255 characters
Value in a number field 9,999,999,999,999.99