Setting up hot corner + expose effect in XFCE was already discussed somewhere else here http://forum.xfce.org/viewtopic.php?id=8105, so I could not claim I'm first in that respect.
However I could not find step-by-step solution for Linux Mint, thus I'm sharing the steps here.
1. Install brightside (via Synatic Package Manager or apt-get).
2. Install skippy-xd (https://code.google.com/p/skippy-xd/). You'll need to compile from source for this one.
- Download the source (https://github.com/richardgv/skippy-xd)
- Install required development packages (https://code.google.com/p/skippy-xd/wiki/Installation)
sudo apt-get install libimlib2-dev libfontconfig1-dev libfreetype6-dev libx11-dev libxext-dev libxft-dev libxrender-dev zlib1g-dev libxinerama-dev libxcomposite-dev libxdamage-dev libxfixes-dev libxmu-dev
- Extract the source (unzip).
- cd into the source folder, then
sudo make install
which would install skippy-xd into /usr/bin
3. Run brightside-properties, and set Custom action... > On entering region to skippy-xd.
4. To wrap things up, add brightside to your list of Application Autostart.