SKYPE - I don't care this much, or can I say, at all.
Loading speed - Yup I've see this over the net, like very significant.

Other than the above 2, anyone got additional info?

I think PSP2000 have 2 additional functions (PlayStation Spot and 1-Seg) compared to the others and these functions only work in Japan. 1-Seg requires "1Seg" TV tuner (model PSP-S310) peripheral addon. These functions are also available on other models with custom firware by setting Fake region to Japan.

Another difference is it's region code. PSP2000 is Region 2 and PSP2006 is Region 3. With original firmware you can only watch region free or Region 2 UMD movies with PSP2000. You should be able to watch UMD movies of any region with custom firmware, but I've come across some UMD movies which only works on PSPs with the specified region.

This number indicates the intended region the unit was designed for. These model numbers are as follows:
PSP2000 - Japan
PSP2001 - USA
PSP2002 - Australia
PSP2003 - United Kingdom
PSP2004 - Europe, Middle East, and Africa
PSP2005 - Korea
PSP2006 - Hong Kong
PSP2007 - Taiwan
PSP2008 - Russia
PSP2009 - China
PSP2010 - Mexico

Most UMD Movies are region locked. I think the regions are:
Region 1: Canada, U.S., U.S. Territories.
Region 2: Japan, Europe, Eastern Europe, the Middle East.
Region 3: Southeast Asia, East Asia (including Hong Kong)
Region 4: Australia, New Zealand, Central and South America, Caribbean
Region 5: Former Soviet Union, Indian Subcontinent, Africa (also North Korea, Mongolia)
Region 6: China

credits: bill3