Is it safe to to upgrade OS X 10.7 to 10.8 on a productive system? I was wondering if there are any implications to upgrading my iMac web development machine (which is highly configured MAMP (Apache, MySQl), customized hosts file, custom Network Card settings, etc... from OS X 10.7 to OS X 10.8?

Will I loose everything 9apps/files/MAMP config, etc...
Most of the time the OS X upgrade routines work quite reliably and in this case there shouldn't be any deal-breakers like Rosetta back in the days. However, it is impossible to tell for sure. What I usually do, is to clone my system to either a second partition in the internal drive or to an external (USB) drive (using a tool like SuperDuper! or Carbon Copy Cloner).

After booting the clone (press alt in the boot screen) you can safely upgrade this partition to a newer version of OS X and play with it for a while. Once you are sure everything works, you can either copy it back to your main partition or upgrade that one too.

Nevertheless, I recommend to have another (e.g. TimeMachine) backup available, in case anything goes wrong.