[wp-hackers] Where Should Plugins Store Files?

[Raj]

Often times I find my plugins require file uploads and a location to save
them. Other times I generate image files.  So far I have been base64'd them
and putting them into the database for fear of lack of permissions in the
file system. Surely there is some location within wordpress where a plugin
can rely on having some place to put files? wp-content/uploads may be? Can I
rely on wp-content/uploads to always have read/write permissions be the
location where files can be placed if necessary? Please suggest how I can
approach handing writing files to the file system.