Jeffrey Snover posted (back in November of 2007) a script that solves the "PowerShell starts slowly" complaint that I and others have run across.  It turns out that while the PowerShell installer is supposed to run 'ngen.exe' to convert assemblies into platform-native code, it either happens slowly or somehow gets forgotten.  Running his script will manually kick 'ngen.exe' into running on all of the PowerShell-loaded assemblies, dramatically improving startup time.  For me, startup is now almost instantaneous!