No, the W7 Disc Cleanup does not clean Flash, but you can clean Flash from the Control Panel > Adobe Flash.
Assuming you trust Adobe to get it right.
I use a script to run FF and when I shut FF down, the script runs CCleaner.
I had an annoying experience which (I think) was caused by left over garbage in the Internet cache.
I don't know if a 3rd party defragger knows any better then MS about where to place files. They all tout that they "optimize by placing files at the fastest part of the disc", but I just don't know.
The Windows 7 defragger doesn't give any indication of what it is actually doing.
If you ran the XP defragger, you got a little picture of what it was supposedly doing.
However I've noticed that it often leaves "holes" which other files can be written into, thus becoming fragmented.
This means that you regularly have to run the defragger.
A more effective way to defrag (it can be time consuming though) is to copy all of the files off of a partition.
Obviously you need to delete everything off of the partition, once you are sure that the copying process was successful.
Then copy the files back again.
They should then form a "solid block" of files.
If those files aren't modified (or deleted) that area should remain fragment free.
I'm not sure that is safe to do with your OS partition.
Obviously you'd have to do that from "outside" Windows.
If you want to try it, remember to make a backup first.
If you are really paranoid about fragmentation, you should defrag your drive,
before installing new programs.
I don't believe in "optimisation" claims (for real world PCs).
I suspect that you could do it, if your system was static (i.e. no files being added/deleted/modified).