An interesting round-by-round comparison of Picasa and WLPG, including this observation:

When it comes to speed, Windows Photo Gallery wins over Picasa by a huge margin. Picasa, in the last few months, has become extremely slow – the software sometimes even freezes while importing new media content into the library. Windows Live Photo Gallery is lightning fast when you compare the start-up speed or when it process new photographs.

Full post: Google Picasa or Windows Live Photo Gallery – Which is Better? at Digital Inspiration – Software Reviews, Internet and Technology Guide.