DD will obviously not give you all answers you need to solve performance/page load issues (for instance you might have to talk to your SQL guru to optimize T-SQL queries or C# developer to optimize their webpart algorithm or tell your end user that they have put too many webparts on a page). In the end it will make the life of any user and a lot easier to understand page load in SharePoint 2010 and hence Project Server 2010.
Script to turn on/off DD (not do not turn it ON in your production server since it will activate it for all pages for all users in your farm!) (copy and paste in a file and save with .BAT extension then execute in your farm):
@SET UTILS_ROOT=C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\BIN
@echo ENABLE Developer Dashboard
"%UTILS_ROOT%\stsadm" -o setproperty -pn developer-dashboard -pv ondemand
@echo DISABLE Developer Dashboard
REM "%UTILS_ROOT%\stsadm" -o setproperty -pn developer-dashboard -pv off