I've been goofing around with Illustrator's auto-graphing features and I have to say I'm fairly impressed.
There's a whole hell of a lot that it won't do (no calculations within data cells, for instance) but then again, there's a lot that I've never been able to get Excel to do either (tasteful color selections, careful kerning, etc. etc.) I'd say that the design team made a carefully-weighed set of tradeoffs: just enough graphing abilities to give us the feature, not so much that you'd want to do your primary number crunching with it. Actually, Excel open in one window, pasting into Illustrator in the other is a combo that's hard to beat.
Oh, and if you find yourself having to do graphs in Illustrator? Download the PDF Workbook from IllustratorAnswers.com. It's concise, thorough and readable. And, please do leave a comment if you read this and have any cool Illustrator-generated data graphs that you'd like to share.