Well, giving my personal account, the off-by-one and off-by-two errors are minor details. The things that really annoyed me were:

1) indexing using () instead of [], which goes against most modern/popular languages

2) how poorly formated / indented / organized is most of the code you find (which is the product of most code being written by non CS people)

3) packages often come with a price tag. I used it as part of a big university domain, so I didn't have to pay for any of it, but it is pretty sad to know that if I were to use it on my own I would have to pay for any missing feature.