to be 100% honest with you, i have only felt paranoid 1 time after smoking, and it was because i was in high school and i was afraid my parents were going to come home early and catch me. i guess it's all about your state of mind when you smoke. if you have a relaxed state of mind and are looking forward to smoking, i dont think that you'll ever feel paranoid.
also, i have never experienced short-term memory loss, nor the feeling of not being able to keep track of time. if i do lose track of time it is because me and my buddies are having too much fun to be worried about what time it is. i smoke on average 3-4 times a week, although i sometimes go for weeks w/o smoking and there are some weeks when i smoke everyday.
you can't let weed become the center of your thoughts, but if you've had a hard day at work/school and want to just chill out with some friends, then that should be okay. i sometimes use weed as a reward, that is, i will say to myself "if i finish all of my homework before 10 p.m., then i'll smoke before bed." things get accomplished that way, at least, for me.
some people shouldn't smoke, like those who are normally paranoid, depressed, or have a highly addictive nature. i guess weed affects everyone a little different, but i really haven't experienced any adverse affects. hope this answers some of your questions.