This self-respecting slashdotter doesn't e-file for two reasons.
First, there is no technical need for an intermediary to receive and forward my data to the IRS. Nobody seems to acknowledge that involvement of intermediaries means there are more interfaces that might be hacked to reach my data. No thanks.
Second, the reason that there are even intermediaries is that (and I wish I could cite a source for this but it's too long ago, mid-1990's) when the IRS originally proposed that taxpayers file directly, the software lobby successfully argued that removing the intermediaries would result in the loss of jobs. The government didn't want to cause job loss, so it caved and now requires those intermediaries.
My tax filings are on paper to protest the idiocy.