I find myself making excuses to go to Voltage often. It has the most peaceful, relaxed ambiance of any cafe I’ve been to. The indoor seating space doubles as a mini art gallery, and they swap out collections every couple weeks or so. Plus, there’s free wifi (well, I think it’s like an hour for every dollar you spend or something, so basically more wifi than you’d ever need).
Although Voltage is nominally a coffee shop, (I usually can’t stand coffee with cream or sugar, but their lattes are seriously so interesting and delicious I can’t pass them up), they have a nice selection of teas too — I think they use MEM tea, which seems to be pretty popular around Cambridge. You get it in an adorable little teapot, which sucks if you’re bad about letting tea overbrew, but it’s nice to be able to control your steep time.
Oh, and they have excellent pastries and snacks. You have to get there early to grab their sandwiches before they run out, though.
I’ve never purchased Teavana tea — it’s overpriced, and too sweet for my liking. Great store, though. They have well laid-out, attractive displays with a really nice selection of teaware, from a variety of tetsubin and yixing teapots to more modern ware, and some awesome teapot warmers. It’s fun to stroll around in there while tasting samples.