Ans- "ReadyBoost is a disk cache component of Microsoft Windows, first introduced with Microsoft's Windows Vista in 2006 and bundled with Windows 7 in 2009. It works by using flash memory, a USB flash drive, SD card, CompactFlash, external hard drive or any kind of portable flash mass storage system as a cache. ReadyBoost is also used to facilitate SuperFetch, which allows it to perform analysis of boot-time disk usage patterns and creates a cache which is used in subsequent system boots." Source
If you are using a high configuration PC, It doesn't show any effect on speed because if you are a normal user I think only a few times you use your full ram memory but if you are using an old pc with low ram memory(Like 512 MB or IGB) and harddisk & using vista or 7. It speed up your PC and you will see the result, reduced application data loading time, reduced shutdown and restart time and many more you can't imagine without High ram memory. How to use this feature
Plug in your pendrive-> Format with NTFS or FAT32
Now go to properties->Select ReadyBoost
Check Use this device->Choose maximum space to reserve system speed
Click on Apply and OK. Your readyboost PenDrive is ready Now to Use.
Here is an personal suggestion HP and Sandisk is the Best for this work so what are you waiting for.