Are 2GB of mem even necessary for a notebook?

Intel Core Duo L2400 (1.66 GHz) Processor
100 GB 7200 RPM HD
etc., etc., etc.

In what kinds of circumstances would notebook users even need
2GB's of memory? Just curious.

Thanks a lot, gents.
Now, what about my processor question?
Why the huge leap in price when going between GHz?
1.66 - 1.83 - 2.00 - 2.16?
T2300 - T2400 - T2500 - T2600?

Are the differences that observable?