I lived in Beijing for four years and loved every single minute. Some more than others, of course, but overall it was a fantastic experience. Getting around was easy; taxis are abundant and cheap. Knowing a few basic phrases was helpful (turn left, turn right, stop, etc.) After a while you learn some of the place names and you could use those to help you as well; say one of the names you know that's close to where you actually want to be, then give the driver directions from there. You can also get taxi books that list tons of places in Chinese so you can just show your driver the name of the place you want to go; they have taxi books as iphone apps now as well. The subway system is limited, but it was helpful depending on where you wanted to go, and it was ridiculously cheap, as well as being clean, easy to use, and not that crowded.
I found the Chinese to be very friendly and welcoming; more than I expected when I went. Most have no English, but as an earlier poster said, in most of the markets, tourist attractions and expat restaurants, the employees have enough English for you to communicate. Most restaurants have menus in English or with pictures so you can still order.
There is a huge expat community in Beijing and there are tons of things going on. You will never be bored and will be able to make friends if you make an effort. There are lots of expat-friendly restaurants, great bars, food stores with Western groceries. I really didn't miss anything while I was there, but there's tons of food I miss from Beijing. You will eat food like you've never tasted before and you will never be able to stomach food court Chinese again!
Shopping was fantastic and never-ending; antiques, silk, jewelry (pearls!), carpets, furniture, tailored clothes, knock-off bags and shoes, DVDs - I really just finally had to leave because I was shopping myself into a stupor! There are also tons of temples, parks, etc. to visit - you could never hope to reach the end of exploring Beijing.
The major downside is definitely the pollution. Most days are fine but there will be several days a month that are absolutely horrid and you can't believe you're actually breathing that air. But, it does make you appreciate the nice days even more. Some people hated the winter, but it didn't bother me. It does get quite cold (probably comparable to Chicago temperatures), but it's very dry so there's almost no snow and you don't have to worry about icy sidewalks, clogged roads, etc. It's also a bright, clear, sunny kind of winter. Spring and fall are lovely, summer is gloomy and muggy and rains a lot but I was usually away during most of the summer.
In short - I miss Beijing all the time and would love a chance to live those four years again. Take the chance and you won't regret it!