Bootstrap.dat on Mac OSX 10.9 - Difficulty
In the Finder, click the 'Go' menu and choose 'Go to folder' (or just cmd-shift-G)
type 

~/Library/Application Support/Bitcoin/


in the field that appears, click go and viola. If you've never previously run bitcoin the directory won't be there but you can go to 

~/Library/Application Support/


and create it.

the problem you were having trying to find it if you were using the Terminal to do so may have been that spaces have to be escaped in file paths, so the command to change to that directory would be 

cd ~/Library/Application\ Support/Bitcoin 


note the backslash before the space. As I've noted you know, you can also drag files or folders in to the Terminal and it will automatically enter the path to that file/folder.