What steps will reproduce the problem?
1. Install snipMate in Windows (gVim 7.3)
2. Place your own "snippets" folder in c:\vim\vimfiles (or anywhere in your $RUNTIMEPATH)
3. No snippets are loaded.
Snippets will not be loaded in Windows if the first path in a list of paths ends in a backslash. See :h globpath, it reads:
"Note that on MS-Windows a directory may have a trailing backslash, remove it if you put a comma after it."
My quick and dirty fix for this issue is to amend the main snipMate.vim plugin file on line 24 where snippets_dir is set to read:
let snippets_dir = substitute(substitute(globpath(&rtp, 'snippets/'), "\n", ',', 'g'), 'snippets\\,', 'snippets,', 'g')
This substitutes "snippets\," with "snippets," which should only affect the found snippets directories that have additional paths following them. I'm sure there are scenarios where this doesn't do what it's supposed to depending on the circumstances.
A more thorough fix might inspect +shellslash and/or &shellslash to determine whether a replacement needs to be done.