Interesting new features in Leopard
Now that Mac OS X 10.5 (Leopard) is due to be released in 26 October, everyone is curious to see what is new in this version and upgrade as soon as its released.
Among the many new features, there has been a few of them that seemed interesting to me:
Create Instruments with DTrace
Monitor system activity from high-level application behavior down to the operating system kernel, all thanks to the power of DTrace and the instrument builder.
Sounds familiar? Yes, its the same DTrace you know from Solaris (also in FreeBSD). It would be very interesting for system developers to get the best out of OS X core system. Of course, there is an eye-candy interface for using DTrace called Xray.
Self-Tuning TCP
Let Leopard adjust TCP buffer size automatically. Get optimum application performance, especially in high-bandwidth/high-latency environments.
Using a BSD kernel, OS X already enjoys a fine-grained TCP/IP protocol stack, which supports latest enhancements and extensions. This self-tuning feature will definitely improve the network throughput in many situations. However I hope this can be disabled since some expert users prefer to configure the low level TCP/IP parameters based on their experience.
Application-Based Firewall
Gain more control over the built-in firewall. Specify the behavior of specific applications to either allow or block incoming connections.
This one was really missing in previous releases and many people were relying on Little Snitch to achieve this feature. Of course I believe brilliant people in Apple were smart enough to make it so it does not annoy users like windows firewall does.
Sandboxing
Enjoy a higher level of protection. Sandboxing prevents hackers from hijacking applications to run their own code by making sure applications only do what they’re intended to do. It restricts an application’s file access, network access, and ability to launch other applications. Many Leopard applications — such as Bonjour, Quick Look, and the Spotlight indexer — are sandboxed so hackers can’t exploit them.
Something that I am sure has equivalent in Windows, almost like running an application in a chrooted environment. However it sounds more complicated. This will hopefully improve the security in application level and reduce application level exploits (buffer overflow,...) risks.
Multicore Optimized
Take full advantage of modern architectures with multiple processor cores with improved scheduling, memory management, and processor affinity algorithms.
OS X was obviously not optimized for multi-core systems (despite the fact that apple has been shipping multi-core systems for more than a year). This enhancement will definitely improve the core system performance by getting the most out of processor power.
Conclusion
After using OS X for more than a year now, its my favorite Desktop environment. I like the eye-candy user interface while enjoying enterprise grade FreeBSD system core. I cannot wait to upgrade to the latest release, but I am certain that it is worth to wait a few days more.

Might be a little off topic but do you have any experience with desktop bsd distros like PCBSD or DesktopBSD? What's your take on them?
Kamyar: Yes, I do. But I do not use them constantly. However I believe PCBSD is more advanced and user-friendly comparing to DesktopBSD. I like their PBI concept :)
i recommend, installing it on an external hard drive and booting your apple laptop with USB into the new OS X. You can enjoy the new features and evaluate them, and install it on the local hard drive only when you are sure.