Solaris Strengths and Features

chimonm In no particular order

Technical

Stable ABI & DDI
Guaranteed binary compatibility beginning with Solaris 2.6
Great SMP support. IE: Scales very well
DTrace allows production-level instrumentation of user- and kernel-level processes
ZFS - 128-bit, endian-neutral filesystem and volume manager all-in-one
Multiple-platform support (SPARC, AMD, Intel) - other platforms enabled via OpenSolaris.org such as (PowerPC http://www.opensolaris.org/os/community/power_pc/)
- Easily supports multiple variations on an architecture without complicated build or toolchain issues (i.e. 32-bit and 64-bit on SPARC or x64)
Reputation for reliability (Solaris is a more stable OS, especially under high load)
SMF - service management facility
Zones - Resource management (Very lightweight virtualization)
Performance (Many open source applications run on Solaris better than on Linux)
Security, For a long time Trusted Solaris was the standard for a secure UNIX operating system (Solaris 10 onwards Trusted extention is a part of Solaris now available for AMD64/x86_64 platform)
Interesting processor/platform choices (sun4u, sun4v, AMD64, x86 and x86_64).
Has rich set of Debugging tools
- proc tools (pargs,pgrep,pkill,plimit,pmap,preap.. etc) ...
- mdb (live, safe kernel debugging)
- truss (single tool for tracing your apps)
Source code is well documented - partially available here http://src.opensolaris.org/source/

Large ISV support. Almost 5000 commercial apps
Support seems better than competition's
Long product life cycles
Lower maintenance cost
Single neck to choke (There is some debate on whether this is still valid as more FLOSS is included in Solaris)

Learning Solaris opens the door for administration of big Iron SPARC servers
Sun plans to open source all their software
Solaris is being open-sourced. OpenSolaris partially indicates Solaris directions and various distributions are available - http://www.opensolaris.org/os/about/. Opensource Roadmap available here: http://www.opensolaris.org/os/about/roadmap/
It's cool to be different
"Feature creep" is ~~less pronounced in~~ Solaris