1. readyboost will really start working when 4gb of flashram is built into mothervoard designs, and fits a tight specification that guarantees a perfomance boost.
2. Readyboost can enhance your machine perfomance, but its no plug and work first time solution, and mainly only works for lots of small 4k random reads and small random write perfomance, boosted by faster access times.
3. Make sure the stick or card you use will run at sufficent speed to meet the defined perfomance criteria as discussed int he prevous SD card post, a class 6 card will guarantee some performance but even these vary massivley.
4. Upgrading to a Faster drive 7200rpm or a higher density 5400rpm drive or More RAM will have much larger perfomance gains overall in comparison to readyboost on a system with low ram and a slow old drive 60gb or less etc. Readyboost certainly does help if you cant afford more ram and want to enhance say 1gb or less memory machine perform better under heavier load.