My personal answer: never. Google has killed free apps that had had lots of users for years. If Google can't guarantee that a free app will stay free and available, nobody can.
None of the above is communicated when you say "it's free!" on your front page with no other explanation, or when you ask "how long does it need to be provided for free before you trust that it will stay that way?". The critical factor is not how long you've been providing it for free; it's that the free "product" is not really the product, it's just a side effect of your real product.
If you really want to change people's attitudes about the issues involved here, find a catchy word that differentiates your business model from "free".
Threads in topics often vary in subject. My posting would not be suitable as a reply to the OP, following from the top of this thread, I would say my replies are perfectly reasonable relative to the parent post.
I still think an answer to my question about hellosign's business model would be of interest for this thread, but obviously if you're not involved with hellosign you can't give that answer. Sorry for the misunderstanding on my part.
Yes, I am taking on a potentially bad burn of Google ever axes gmail or cuts some important features (it's happened to me with Hotmail before), but I'm willing to take that risk because of the gmail feature set.
At some point, Hotmail decided to delete sent/received email older than some arbitrary amount. An important personal conversation to me was deleted.
It's not about the duration of "Free", it's about the emergence of a recognizable business model, and also about the general complexity of the product and how frequently I would use it and come to rely on it.
Another issue is that we all know that nothing is "free", and as the saying goes "if you're not paying for it, YOU are the product". I don't like the idea of business documents with my signature somehow ending up in an ad-based business model.
B2B sales models and tactics are (IME) very different than B2C. On the plus side, B2B is more likely to be receptive to a paid-for product, and the down side it can be somewhat more difficult to get the viral exposure you get from a B2C product since not as many people are likely to be interested in it, or able to decide for themselves if they can use your product.
A freemium model works good here. Have pricing set upfront and clearly defined. Let me test the product with no risk for some period of time and then convert to a paying customer (or not).