However, I can verify that it’s very useful – streaming is fast and available wherever data is available. Full song/album caching is also an option if you are going out of range for a while (using the official Google Music Android app). There is also a full-featured browser client for desktop listening. Google allows for a limit of 20,000 songs initially.
Note that this service is only officially available in the US, if you are overseas there are workarounds (which I had to employ).