I travelled to Amsterdam with Eurolines. I was a bit concerned about the length of time (12 hours), but I was so in need of a break I was willing to try anything. I found it fine.
The outward journey was the best. I checked in at London Victoria, and the wondered what was coming next. The bus left perfectly on time.
The Dutch driver was funny. 'You've made it to London, let's hope we make it to Amsterdam' he announced as we left the bus station. I give him ten out of ten for his honesty in admitting we may not make it. He then announced he was going to play an adult movie. I caught my breath and looked at the two small children sitting opposite me, and at their mother in front of me. He then said '007'. As we went through the channel tunnel, he chatted to me.
Although it was a long journey, we had frequent stops at service stations. We arrived in Amsterdam 1 and a half hours early. The driver was not done yet with jokes. He warned us to be careful about theft in Amstel station. He had seen it before. Someone puts their bag down, turns away for a few seconds, and it's gone. He added 'though for some of you it would be a good thing. It will save you the bother of carrying it'. He had saved the best joke until last. He directed us to the Metro station to get into central Amsterdam.
The return journey was livened up greatly by a party of scouts. Wonderful free entertainment, without them even trying. Shame about the bad tempered English driver. It was fun and games at Calias - someone had the wrong ID. Someone else disappeared at Dover. Nonetheless, we arrived in London exactly on time.
I am using Eurolines again for my following trip. I would recommend it. I know many people have concerns, but really it is not all that bad!