[ikka]

Solaris has their Zones technology, which works EXTREMELY well, and is farther along than the Linux alternatives at this point in terms of ease of use, setup, and ability to finely tune CPU/RAM resource allocation. Not to say that Linux won't get there, though.

[N3WBI3]

I think solaris is worlds ahead of Linux in its tech, and IBM's new stuff (not the OSS they just bought) is even better. The problem is cost for small offices. While Solaris is going X86, that combination is less proven than Linux and IBM has not x86 offering for AIX (that I am aware of). Even with the solaris x86 I'm not sure you can use zones on that setup.

If you have a few servers (smaller ones) you need to pair down Linux is one fo the better soulutions out there (bang for the buck)