I have yet to meet anyone who is a fan! Including a friend who works for them. 
My employer paid a portion of our bonuses in company stock. You could also buy company stock at a discount through ESPP. This appeared as a single account when you logged on, but was actually two accounts / websites under the covers.
When I come to fill in the tax forms that year, I pick the 'download tax forms form' option so I don't need to transfer the details from the paper copy I received in the mail. I compare the number of documents downloaded with the number of documents I received in the post. They number and the first few values I check match, so I figure I'm good to go.
However, the digital download for the brokerage only contained the 1099-DIV for one of the accounts. The paper 1099-DIV contained both accounts, but as two sequential blocks under the same 1099-DIV header. So my filed return doesn't declare all the dividends I received.
So I get a letter from the IRS saying 'your declared income doesn't match what the brokerage reported to us'. It was a ten page document that spent the first 4 pages explaining in clear, precise terms exactly what and where I went wrong, how much I owed, and how to calculate it and dispute it myself if I disagreed. The remaining 6 pages covered payment options.
To me, this letter was proof that, through payroll and banks/brokerages reporting, the IRS knows everything needed to calculate my taxes more accurately than I do. And I bet it didn't take them a whole weekend to do it.
So I love the IRS for the quality of their letter (and for only charging me interest), but hate the politicians who won't let the IRS file for me (or at least pre-fill most of the tax return for me).
