I am running Mountain Lion on a 24 GB ExpressCard (about 3 GB free) with 4 GB of RAM. After upgrading to Mountain Lion I am getting a "Hard disk is nearly full

I am running Mountain Lion on a 24 GB ExpressCard (about 3 GB free) with 4 GB of RAM. After upgrading to Mountain Lion I am getting a "Hard disk is nearly full" message much more frequently. Almost never seen that on Lion. Could this memory management change be the culprit?