I as wondering how much space Mathematica, Maple, and Matlab will take up, under Windows and under Ubuntu? I am planning to reserve some space in partitions.
Mathematica requires 4GB on any platform (Link) Maple requires 1GB on Windows and 2GB on Ubuntu (Link) Matlab States it requires FYI  I used to partition everything, now I don't bother. Forget partitions, it just becomes a nightmare to manage at a later date! 


Since Mathematica 6, but especially with Mathematica 8, using certain functionalities such as curated data (for Chemicals, Geography, Polyhedra, etc.) will load and update local databases from the Wolfram internet web sites. Expect the footprint of the program to grow over time. Usually the first use since install of one of these functions will cause a significant first download and indexing before it answers. 

