As with any application (whether single-tier or multi-tier), security is absolutely critical. Although it's tempting to dig in and start developing the next killer app right away, it's also important to build a good security framework prior to additional development. Otherwise, it's likely that one will miss a security hole or the developer will have to rewrite code in order to fix any security issues.

It is also important to recognize that no developer is perfect; it is vital that your code undergoes many code reviews by many different developers (something typical of open source projects). However, it's also true that should the code base be subjected to many eyes and code reviews, security holes and other issues will still manage to make it through to the final project. Thinking about security prior to writing code can go a long way to ensure a good foundation, but it can't ensure that your product is completely secure.

There's a fine line we walk when...