I took my share of Greyhound trips from Ottawa to Toronto, because it was cheaper than VIA Rail was. The last straw was when the bus that I was to take from Toronto to where I live left two hours early, leaving me stranded in Toronto at 6 AM after taking a 5 hour bus ride from Ottawa. Thank God for GO Transit.
What I really hate about them is that they have a schedule, but not really. They constantly sell more tickets than there are seats on the bus. The good part about this is that since your ticket isn't connected to a bus, you can take one any time on that day. But then of course 200 people try to get on an 80 person bus. It's a terrible mess.
To make matters worse, none of the other bus companies in Southern Ontario actually go to Ottawa, so its Greyhound or nothing.
So now I only take the train. It is always a pleasant trip. Definitely worth the price.