After installing imagemagick and then running $ brew doctor $ brew update I had these errors, hope this helps:

Homebrew error

Onni-MacBook-Air:sample_project onnimonni$ brew doctor
Warning: Unbrewed dylibs were found in /usr/local/lib.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae, and may need to be deleted.

Unexpected dylibs:
    /usr/local/lib/libmacfuse_i32.2.dylib
    /usr/local/lib/libmacfuse_i64.2.dylib
    /usr/local/lib/libosxfuse_i32.2.dylib
    /usr/local/lib/libosxfuse_i64.2.dylib

Warning: Unbrewed .la files were found in /usr/local/lib.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae, and may need to be deleted.

Unexpected .la files:
    /usr/local/lib/libosxfuse_i32.la
    /usr/local/lib/libosxfuse_i64.la

Warning: Unbrewed .pc files were found in /usr/local/lib/pkgconfig.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae, and may need to be deleted.

Unexpected .pc files:
    /usr/local/lib/pkgconfig/osxfuse.pc
Error: Homebrew doesn't know what compiler versions ship with your version
of Xcode (5.0.2). Please `brew update` and if that doesn't help, file
an issue with the output of `brew --config`:
  https://github.com/mxcl/homebrew/issues

Thanks!

Warning: Your Homebrew is outdated.
You haven't updated for at least 24 hours, this is a long time in brewland!
To update Homebrew, run `brew update`.
Onni-MacBook-Air:sample_project onnimonni$ brew update
Error: undefined method `factory' for Formula:Class
Please report this bug:
    https://github.com/mxcl/homebrew/wiki/troubleshooting
/usr/local/Library/Homebrew/cmd/update.rb:61:in `update'
/usr/local/Library/Homebrew/cmd/update.rb:60:in `each'
/usr/local/Library/Homebrew/cmd/update.rb:60:in `update'
/usr/local/Library/brew.rb:95:in `send'
/usr/local/Library/brew.rb:95
Onni-MacBook-Air:sample_project onnimonni$ brew update
Already up-to-date.