Rachel - on her 30th birthday realises she shoudl be with the man she will marry and have kids with at this point and gets frustrated.
Pheobe - in a flash back loses 1 year of her life, celebrating her 30th birthday on her 31st.
Monica - gets drunk on her birthday and makes a speech and then faints
Joey - cries on his 30th birthday and then again at all the others. At the end when he realises he will be 40 in ten years he cries again.
Ross - buys a car on his birthday and spends the whole day trying ot move it. At the end he sees someone much older than him driving another.
Chandlers birthday was also quite funny.
I liked it how Joey had a chidish friend in this episode to ride a scooter with.