I am one of the more successful MTT players here.
So far in 2009, I have won five MTTs outright (one of them joint first in a chop), had one second place, and two other final table finishes. That is from approximately 100 tournaments entered.
Whether you define that as winning "constantly" depends on your frame of reference. I think most experienced MTT players would think it a good win rate. I certainly feel that 2009 has been a good year for me so far.
However, if you look at it from another viewpoint, it is 8 successes and ~92 failures, which doesn`t seem very good. Members of my family who don`t understand poker think I must be crap at it, since I play often and win only occasionally.
The nature of MTTs is that you win when you play a solid game
and when your cards hold up. You need
both to come together on the same day to provide you with a win.
More often than not, you can play your "A" game and take a bad beat and crash out of the game. You need iron discipline and strength of purpose to hold your temper and play the exact same way the next day. If you let bad luck affect your play, you start on a downward spiral towards a place where you can never win.
Making a career out of online MTTs is not for the faint-hearted.