Kevin Frie, development lead for core parts of the CLR recently posted about what CLR updates that come in 3.5 SP1....

• NGen infrastructure rewrite:  the new infrastructure uses less memory, produces less fragmented NGen images with much better locality, and does so in dramatically less time.  What this means to you:  Installing or servicing an NGen image is much faster, and cold startup time of your NGen’ed code is better.
• Framework Startup Performance Improvements:  The framework is now better optimized for startup. 
• Better OS citizenship:  We’ve modified NGen to produce images that are ASLR capable, in an effort to decrease potential security attack surface area. 
• Better 32-bit code quality:  The x86 JIT has dramatically improved inlining heuristics that result in generally better code quality, and, in particular, much lower “cost of abstraction”.

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