When it started in [who knows? See Mark's question on the word's originMark's question on the word's origin] it was, if not derogatory then certainly condescending.
It can be used in a tone of "friendly ribbing", but that's true of other terms that would be considered derogatory when there's no other context to reposition it.
It's not considered explicit, so you could safely use it of yourself in a self-deprecating manner without much risk of people taking offence at the word itself.
To use it of potential customers, you'd have to be confident that the informal and fun tone had already been set. If so, then it could well work, but it could definitely backfire too. vBulletin's default member levels jokingly mock both new and more senior members by having "cool newbie" as the starting level, and "no life" as one of the more advanced levels. Since "no life" would generally also be seen as derogatory, this gives an insight into the way "newbie" can be taken here - it's an insult, but the tone is set so that mild insults are to be taken as a joke. There are businesses that can work with that tone, but most could not.