I use the HTML aware project description text to record File links to network drives for a similar purpose to your need to record links to documents within an issue. In my use case, I like to refer to project related folders and specs by links to shared network folders and/or files.
The syntax that works for me (on both I.E. and Firefox) is:
That should work on any version of JIRA, no need to use 3.4beta Wiki
And I can think of many reasons why a link is preferable to an attachment:
1) A living document may always have different versions and you want people to always link to the most current version
2) It is wasted space to duplicate a file that already exists on a network share, which is (again) considered the master
3) With no option to delete attachments, users will find it difficult to upload new versions.
By the way Nick, your help for Wiki markup says it only works on Internet explorer:
I wonder if you add the 3 additional slashes whether it will also work on Firefox?
Thanks to Neal for this info. The page is now at http://confluence.atlassian.com/x/ZVMC and will be linked from the help page for wikimarkup