Is it really safe to drink caffeine?

Yes. Yes, but you should limit your intake to the equivalent of two 6 oz cups of coffee daily or 1-2 cola beverages.
Yes. Studies have shown that a cup or two of coffee is safe in pregnancy. A small cola or a cup of tea are the same. However, if you have high blood pressure you should avoid caffeine since it may increase your blood pressure even more.
Yes. During pregnancy limit intake to 1-2 servings. Excessive caffine has been shown to cause pregnancy complications. If not pregnant excessive caffeine can also cause problems --hypertension, GI problems, and insomnia.
Yes. A moderate caffeine intake, such as two 8oz cups of coffee per day, is probably safe. However, caffeine is a diuretic which means you'll need to increase your water intake to make up for the excess you lose. Also, drinking caffeinated beverages will cause you to have to urinate more often which is already a problem for most pregnant women.