I currently use CentOS for on my server, and I've been trying to figure out the practical differences between Linux and OpernSolaris. I'm not a linux master, I merely know my way around the system and can generally install things if I need to (though I won't lie, I get tripped up on that sometimes).
If I switch to OpenSolaris, are there going to be major things that I am unable to do now or that at least won't work the same way? My stacks mainly just consist of PHP/MySQL or Node.js/MongoDB.
OpenSolaris is being forked to OpenIndiana, and I would highly recommend using the later, as Oracle has a tendency to close up previously-open projects. Otherwise,
OpenIndiana/Solaris Pros:
Cons:
Other differences include file system structure, command naming and syntax, etc. There are a few good articles on the difference if you google "linux v opensolaris;" eg: http://linuxhelp.blogspot.com/2009/09/open-solaris-vs-linux-comparison.html, http://tuxradar.com/content/opensolaris-vs-linux
SAMP (solaris, apache, mysql, php) stacks should run just fine, assuming your hardware is all supported.
We've recently moved our system from CentOS to a managed Solaris environment. As well as the typical differences @Bryan mentioned, we came across a very strange problem.
Some of our legacy code used bitmaps to essentially "join" database records. We had some queries that calculated the IDs present in the bitmap and join the included rows. This worked fine on CentOS (albeit rather slow) but Solaris was a different matter. Cutting an even longer story short, we found the problem on Solaris was floating point precision - Linux can work with very large integers with a slightly higher precision than Solaris.
I'm not a system admin, so I can't really go into more depth than that, but I can link you to this paper on Floating Point Arithmetic which will likely explain the possible problems better than I have.