Below are some screenshots of a few of the bundled scientific applications.
This is BOINC, a program for utilizing spare CPU cycles for scientific research purposes.
XDrawChem is for plotting out chemical compounds. Here I am goofing around with it. :D
Speaking of goofing around, this is Ghemical. You can create chemical compounds here, in 3D, and spin them around in amusing ways.
Data Explorer is some kind of data entry program. Not sure if it is similar to a database or a spreadsheet as I couldn't get it to do much.
OpenUniverse is an Earth simulation program.
QtiPlot is for plotting various graphs.
Apart from the scientific programs bundled by default and the neat theme, there is no difference between Poseidon and Ubuntu.