Share your experience!
RAM memory is volatile.If you restart,how much do you get?
512 MB isn't that much and it does not mean that if you have more RAM it will be better.Android needs RAM occupied so it opens apps faster.
I would advise you to keep away from any kind of battery savers,task killers.
thank you very much thats what i need to know i read somewhere that there should be like 100MB of RAM free and i had no idea how could i do that when i am happy if at least 50MB is free 
i noticed one strange thing. When i run phone in safe mode amount of free RAM is around 100MB but when i uninstall all downloaded apps and even some preinstalled like facebook (very memory hungry) i styl cant get more than 70 to 80 MB free but since its aparently the same on all xperias E1 its not a problem
i hope that crashing of some games (like metal slug X) is only problem of poor writen app and not phone itself
Why should we avoid using task killers?
Because they can stop system processes and your device will not work properly.