[jaclaz]

But remember (actually remember to your founder/CTO/whatever) that the moment enough people get pissed off, growth will stall, particularly in a niche market, word of mouth is relevant.

Before being allowed to have (too many) pissed off customers you (your app) needs to be unreplaceable (or have much worse or no competitors).

If on the other hand you would expect to have no pissed off customers, you will need to reduce your expectations.