Mac OS X features a Downloads folder in the user’s home directory, which is where Safari deposits downloads by default. I quite dislike it, and change the download destination to the Desktop right away. Here’s why.
Files downloaded to the Downloads folder are often forgotten. Not only does this consume storage space quickly, but those files are stored out of sight. It’s easy to forget about files acquired during the hustle and bustle of work. Worse is forgetting the task associated with that file, should you fail to capture that aspect on paper, in an app, etc.
Searching the folder is another headache. You can’t, unfortunately, sort by date of download. On Windows you can, as the “last modified” file date as displayed by Explorer represents the date that the file was downloaded. A simple sort will help you find that PDF you downloaded last Tuesday, for example. On the Mac, “Last Modified” could mean the last time a change was made to a given file.
It’s my practice to tell Safari to place all downloades on the Desktop (Safari > Preferences > Save downloaded files to). That way I’m forced to look at each file daily, decide what is, determine what action needs to be taken (including throw it away) and take it.