Wow, is about all I can say.
I have been a hardcore Linux user for 8+ years, and have dabbled in an out with Solaris as my jobs have required. A few months ago I grabbed a copy of Solaris 9 x86 and started playing around.. . .not a few weeks after that I thought "what the hell" and put a copy of Solaris 10 beta on my laptop.
I am not one of those people that preach one way or the other for BSD, Solaris, Linux, etc, etc. . I see all of their strengths, and weaknesses. They are all Great OS's and have their purpose.
Lately I have been testing out some of the new features in 10, and have been quite impressed.
N1 Grid Containers - rocks. Much the same as when I would set up virtual servers in Linux, but appears to be a little more solid. I have purposely crashed my test Zones on several occasions, and am pleased to say the Global Zone has never winced once. Ohh, and in my opinion setting up a Zone in Solaris 10 is easier then a virtual server, or even a chroot environment in Linux.
ZFS - wow, an amazing advance in file systems and storage. I have not played much with it yet, but the implications are almost endless.
Dtrace - take truss or strace pump it up on steroids, throw in a little C syntax and there you are. I'm still going through the guide on this. .but it has been pretty easy to pick up, and I have been impressed with the potential for this new tool.
http://docs.sun.com/db/doc/817-6223
Janus - Nice, nice. .I have had little problem so far. I mostly compile all most apps locally on each box, for what every architecture it's using. But. .it's nice if you don't need to as well ;) Some ideas I have read about are using an N1 zone to run a completely functioning Linux env inside Solaris. Or just run Linux apps side by side your Solaris native stuff ...your choice.