It's highly probable Apple computers (i.e. Macs) will use flash cashing. Maybe not for booting, because you don't really reboot a Mac as often as a windows system, but more as a cache between the RAM and the hard drive. Safe Sleep on my Macbook takes a few seconds, because the RAM content (2GB in my case) has to go on the hard drive. It's already fairly fast, but with Flash Memory, it could be even faster.
Also the swap files (when your RAM is full but your applications need more memory, the hard drive is used as RAM too, but a very slow one) could easily be put on flash Memory. That would give you a tremendous speed boost when multitasking, kinda like having loads of RAM. 2GB of RAM plus 4 GB of Flash Memory would be affordable I think.
Some Hardware Manufactures already have hybrid hard drives that have the flash memory built in.