There was a Sporting News articles some years back that estimated that 2/3 of all MLB ticket revenues were from corporations.

I worked for a large Minneapolis area corporation (Cargill) in the 1980s and 1990s, and they owned literally hundreds of season tickets for all of the local sports in addition to luxury boxes. I also had suppliers as far away as Texas who also owned multiple season tickets for the Minnesota teams. I had access to tickets and suites owned by Cargill, Burlington Northern, Union Pacific, General American, Prudential, General Electric, General Mills, Purina Mills, Pillsbury - too many to name.

Corporate tickets enabled me to attend the 7th games for both of the Twins' WS championships. For the 1991 final game, I was the guest of two guys from the Canadian National railroad, and they both left in the 3rd or 4th inning - they said they weren't interested in baseball, they just wanted to make sure I was situated and enjoying myself before they left.

I enjoyed the freebies at the time, but in retrospect I really dislike the whole practice, and think it's been the single biggest contributor to the high prices of tickets today. I'd like to see corporate ticket ownership disincentivized, but I'm not sure if even eliminating it as a tax deduction would solve the problem.