Here's my .tfignore exactly. It is in the root directory of the branch and committed to TFS, but it is never honored. I imagine I'm missing some syntactic subtlety not clear to me from reading TechNet's article on the .tfignore file, but what?
### Team Foundation Server Source Control Ruleset Overrides for the Web Project
### These are created to ensure the proper files for the BEC Website end up
### under control.
## INCLUSIONS
# It is truly silly that VS excludes "Debug"...
!debug
# Include any binaries from sources, because they're all third party...
\sources\*.exe
## EXCLUSIONS
# Exclude site-specific tmp, cache and log folders...
wwwroot\administrator\cache
wwwroot\administrator\log
wwwroot\cache
wwwroot\log
wwwroot\tmp