.NET 3.5 SP1: Changes Overview

Here's a great article describing the changes in details that where done on the framework.

Quick summary :
# Assemblies        112
# Namespaces     919           to  935             (+16   +1.7%)
# Types                39 988      to 40 513        (+525   +1.3%)
# Methods            387 421    to 386 790      (-631   -0.2%)
# Fields                 241 567    to 246 795      (+5 228   +2.2%)
# IL instructions  8 598 933 to 8 620 940   (+22 007   +0.3%)