I'm very unimpressed - I had high hopes alas, here are some real queries from my lab where google gives me the right answer within 1-2 links. (or I can reach for the CRC handbook) W|A Q: speed of light in glass A: c (speed of light) and small glasses are not compatible Q: magnetic moment of cobalt atom A: wolfram alpha isn't sure what to do with your input (note just "cobalt" has the information but you have to dig a…
In this respect it feels like the sort of thing that has always annoyed me about expert systems: it's useful to the extent that you are already familiar with what data is curated therein, and want a handy way to look it up, but rather frustrating for surfing and exploration. I do like it...but I can't help sharing some people's view that it's sort of an ad for Mathematica.
It will find a use as citation source - you can embed statistics or factual info in your web page and reference Alpha, in relative comfort that the data there is factually correct. On the other hand, the lack of specificity in the citation info means it won't be quite adequate for academic use, at least not just yet. Might be that its best market will be among high school students who will a) buy Mathematica later and b) grow up with Alpha as past generations did with their slide rules or TI calculators, and stick with it as it evolves.
I didn't take time to play with the API yet - superficially it looks flexible, but I'm only a hobby coder. Much depends on where Wolfram draws the line between openness and proprietary use.