It'd generally be helpful if you have a system with limited memory. ReadyBoost acts as a cache and accelerates the memory paging-in operations.
A functional NLE workstation should not start out with this in mind. You'd want your NLE system to have a comfortable amount of memory (for Vegas, probably 4GB is a good number to start).
I find that after ReadyBoost has been running for a while and has learned your program launching habits that programs load significantly faster with it than without it.
I just upgraded to Win 7 about a week ago, and after discovering ReadyBoost and decided to give it a try. After a frustrating 1/2 hour of trying to get the tabs to come up on the dialogue autoplay and searching all windows help, I found out that not all memory sticks are compatible with ReadyBoost.
The post I read said it wasn't all that effective, so I'm just going upgrade my system from 2gb to 4gb and call it even.
Once you've got 4gb, I don't know if they will be utilized?
ReadyBoost is also used to speed up SuperFetch, the updated version of Windows XP's prefetcher which performs analysis of boot-time disk usage patterns and creates a cache which is used in subsequent system boots. It does speed thing up even if you have a fast machine with plenty of RAM. If you have a flash memory stick that's compatible with ReadyBoost, just plug it in and be done with it, it certainly won't slow anything down.