Flash drive "speed"

I've seen flash drive speed discussed in terms of read/write data transfer rates, which I can understand if I'm transferring large files. But how does it relate to launching and running programs, which is what I really care about?

What's important to me (and I would spend $$ to speed up) is the time needed to launch and start using an app.

When an app is launched, is it read into RAM and executed there? If so, I can see that transfer rate is important. Or, does it run on the drive? In that case does advertised "speed" relate to program execution?

What should I look for when buying a flash drive that will be used to move into and out of applications as quickly as possible, rather than to store large data files?