I am new to Unix/Linux and corrently setting up a Debian Wheezy server for my domain name. Here and there I find useful tutorial on how to do this-and-that, but I am not sure where I can find a community that reviews those packages for safety and so on. Corrently I am looking for postfix package, and it can be used as an example. I did do a search on Google, Yahho, Bing and did not find anything with reviews, only wikis and tutorials. Which websites can I rely on for safe reviews of such packages? 
Where to verify and review various packages before installing them
debian;security;software installation
You should trust the actual Debian repos for this purpose.This is all about open source software and the community.There are thousands of companies and individuals that trust Debian with its data.If a package misbehaves on purpose (like someone injected a malicious code in there), it is very hard that this goes unnoticed. Even it gets past their testing process, which is also held by the community.Once it causes a problem somewhere, this will be big news and the community will quickly correct the problem. Think about it as a more robust version of Wikipedia, if we can make this analogy ...If you are really concerned and don't want to follow such a model, you can go for a paid linux distro with actual maintenance and support, if this makes you feel more confident. Redhat being a good example for that.