Via here: BizTalk Server 2006 R2 SP1 is now available !!!

These 2 factors are great improvements, or rather - fixes:

Better reliability, performance, and scale for the following key features

• Throttling and dehydration of orchestrations.
• Archiving and purging operations.
• BAM alerts and archiving.
• HIPAA.
• Reduced memory consumption in scenarios using scripting functoids.
• Improvement in the bts_FindSubscription stored proc, resulting in faster execution and lower CPU utilization.

Better management and deployment experiences

• Performance and user experience improvements of key scenarios.
• WCF configuration management.
• Significant improvement in deployment time for send ports using a map.

While still some time away, I am very looking forward to BizTalk v.Next where there will be some very interesting innovations to push the low latency envelope (every bit of pun intended).