I have not much idea how this Snow Leopard will perform. Although at $18 to upgrade, it is certainly not a bad price at all.
The lady at the sales centre told me that this new OS occupies something like only 9Gb (instead of the usual 16Gb of Leopard OS) and runs faster.
I am usually not very sure about new OS updates, in case after launching there is some bugs.
Will be keeping my eyes on more comments in this thread.