There are many somewhat 'small' differences (not taking security into consideration where the difference can be huge of course because Solaris has implemented many measures to meet government security requirements for its use on military installations-I attended the training myself about 2.5 years ago).

For instance, the default run state on a Solaris box is run state 3 (multiuser with NFS - meaning that the scripts for starting NFS will be run whether or not you are actually running NFS). The run state on a RedHat Linux box is 5 by default (unless this has changed?)

The directory containing most scripts on solaris is /etc/rc2.d. On Linux systems, the /etc/rc.d/rc5.d directory holds the scripts for setting a run state of 5

Also, there are many small language differences such as useradd (in Solaris) and adduser (in Linux).

I would do a search on google for 'Linux Unix Solaris Comparison' and see what you get. Many online forums can be helpful too.