Open source abdicates your flexibility as a developer to better serve the people who actually use your products. You can see that as a constraint... or you can see it as a door to iteration, innovation, and constant progress.
Two thirds of all of the websites in the world use OpenSSL, this vulnerability would enable hackers (or anyone else for that matter) to exploit the cryptographic library and use that as a way of stealing information trough the SSL/TLS gateways.
The difficult-to-notice vulnerability of Heartbleed had been there for years before the greater threat was announced to the general public. Now that everyone knows it exists, companies are scrambling to fix it.