For those asking about what they are like now, I went to the link to the consumer advice page that was linked to early in this thread. It had a lot of posts that were from the very recent past, IIRC maybe a couple of dozen that seemed to cover the whole of 2016, lots of them talking about exactly the same issues that seem to go back years. In among the negative posts were also some good ones. I guess as with most mail order businesses there are a lot of people who get what they ordered, and that is all they are worried about. You are of course also far more likely to see negative postings, especially on those types of sites, because it it where they angry and disgruntled, who have had a bad experience seem to end up, looking to resolve the problem, or at least to let off some steam about it. Still the litany of very similar complaints, and from all over the world too, since Vistaprint in now a global brand, not just the USA makes me inclined to think that the company still has some issues that have never really been resolved. probably 90% of the customers got what they thought they wanted. The problem is that with a global company the size of Vistaprint that 10% of unhappy customers is a very significant number of folks.
I know enough folks who have had low level issues with using Vistaprint that they would not be anywhere on my list of companies to go to for printing or any other services. Not that using a local design/print shop is likely to be completely pain free either, but at least with local you have a chance to personally deal with the issue face to face.