I just finished reading Tiger Trap by David Wise. I read the whole book (so my "impressions" label isn't really accurate, because I use that for books I didn't fully read). I don't feel like writing an entire review but I wanted to capture a few thoughts.
First, if you know nothing about Chinese espionage against the United States, read Tiger Trap. I didn't think Tiger Trap was the easiest book to read about the subject, but I haven't seen any other source cover so much history in one volume.
Second, it seems the Chinese prefer to use human resources to steal classified information, mainly because accessing classified networks is tougher than accessing unclassified networks. Still, there are plenty of cases where humans physically stole unclassified but sensitive information. Most of these predate the Web however.
Third, the Chinese like to "get good people to do bad things," as I Tweeted last week (citing page 16). In other words, China appeals to its overseas ethnic community to steal information because China "is a poor country," and it "needs to develop." (Oddly enough I have read these exact words in articles by various people who brush off reports of espionage.) While some spies act out of greed or revenge or a need to feel important, it seems plenty of other spies think they are really doing the right thing, leveling the playing field, or even helping both sides!
If anyone can provide the names of other resources describing Chinese espionage, I would appreciate the comment.