In a response to ErstwhileEditor's request for pearl tea shops, I wrote that there is a Lollicup at Porter Exchange. I was slightly mistaken about that; there is a pearl tea stand at Porter Exchange, but it's not Lollicup. Here are all the places I know to get bubble tea in Cambridge:
Tapicha - In Porter Exchange.
They serve a full range of pearl tea. They have black, green and thai teas, 4 milk flavors, and 5 fruit drinks. You can get tapioca pearls or coconut jelly in your tea.
Concord Ave. Cafe - At the corner of Concord Ave. and Walden St.
A nice, eclectic corner store. They don't specialize in pearl tea, so it sometimes takes a bit longer to make. They make espresso too, and also have a variety of (mostly pre-made) food: pastries, lasagna, sushi, sesame noodles.
Dado Tea - 955 Mass Ave (1/2 mile west of Central Sq.)
Not open yet. Their scheduled opening date is 9/21. They're going to be a complete tea cafe. Their menu lists lots of loose teas, pearl tea, chai, Tibetan tea with butter (though I don't think it will be rancid yak butter). They have a website: www.dadotea.com.