Especially when you're using a bootloader, isn't this interval something like 2 seconds? Doesn't that mean that the user has to push the button a long time before the processor can latch it?
Yes, it would be dependent on the specific bootloader used as to how long the bootloader decides to time out and jump to start the preloaded sketch. I've been using the modified Adafruit bootloader for quite awhile sense one benefit is that there is almost no delay at all for the sketch to start on initial power-up. That bootloader also handles WDT interrupts better. Not sure what the delay is on for the new Uno bootloader. Slow to start bootloaders with long startup delays are so 2009. 
Lefty