The harddisk is the slowest subsystem in the whole computer system and it is one of the main reason why laptop have always been much slower than desktop PC. The Size restriction to 2.5″ from the desktop 3.5″ slowed things down quiet a bit.
With Laptop the fastest harddisk rotation speed is currently 7200RPM while Desktop 3.5″ harddisk is available in 10000 RPM. While a show harddisk could be negated with plently of RAM, there is only so much you could speed up and it is usually useful for programs, and if you are trying to view your whole collection of Photo you will definitely notice the speed difference. And hence try to upgrade the harddisk if you already have sufficient RAM.
With the changes in FLASH technology Solid State Harddrive are now available and anyone using it tell you that it is the fastest thing around. But most of us would not be willing to pay for it currently cause of the rocket pricing currently.
And hense the choice would be
7200 RPM drive with around 200G
5400 RPM with 250G or
5400 RPM hybrid drive
The hybrid is only good if you use VISTA with a chipset that support ReadyBoost. However I would recommend a 7200 Drive over a 5400 one.
I decided to upgrade to a SSD if money is no object but ended up with an 7200 7K200 from Hitachi, The speed boost is very noticeable, and the system have become more responsively instantly.
WEI for hardisk is now 5.4 from 4.5 That is a major Boost .