Let's start off with a little warning about Mango Square in general; there are some ladyboys around and if you're too drunk to notice - well. There have also been occasions where people have been drugged. Usually this happens if you flash a lot of money. Keep your big notes in one pocket, and the small ones in another. I've never had trouble here but I advice you not to go alone unless you are familiar with this area. Getting drunk and being alone you might become an easy target. Drunk and with friends you can have a great time.
Mango Square is also a known place for westerners meeting filipinas. Hence, it's also a place where you should be street-wise.
Otherwise, this place is pretty cool. 0-100 peso entrance, depending on what time and day you arrive. Late night it's 100 including a free drink, but if you come early you might come in for free - without free drink of course.

These people are actually sitting at the neighbor bar Numero Doce, Juliana entrance to the left.

See and be seen!

There's a dance floor and lots of tables and chairs all over. If you can't spot a vacant table, ask one of the waiters to do it. If you tip them, you will have extra attention from them. Julianna recently rebuilt the place, moving the bar. Behind the bar there are a couple of private seatings. To sit here you pay like 1000-1500 peso consumable. Good idea if you're a big party, becuause you easily spend this amount anyway. Order some pitchers and snacks and you'll have a good time.
That being said, Juliana is not an expensive place. SML 50 peso, and lots of coctails in glass or pitchers. They also serve some pretty cheap pica-pica dishes, such as crispy pata which the locals like.
Cheers!