Who can use it?
It's a trifle difficult to understand how OWC is licensed when it's only installed on a server for producing static images (for interactive use by clients it's much stricter). Luckily someone asked Microsoft this exact question, to which they (apparently) answered:
Below is an extract from the Office Web Components End User Licence Agreement (EULA) which states that you can install one copy of the software. That one copy of the software can be installed on any device (including a web server) if you already have one of the software licenses mentioned below (such as an Office 2003 Suite licence) assigned to that same device. The software is then used to publish spreadsheets, charts, and databases to the Web.
Here's the relevant part of the Microsoft Office 2003 Web Components Setup EULA:
If You have a valid end user license for Microsoft Office 2003 or any component application of the Microsoft Office System, Microsoft Office XP, Access 2002, Excel 2002, FrontPage 2002, or any other product identified by Microsoft and with which the Software interoperates (the "Licensed Products"), and You licensed the Software from Microsoft, You may use one (1) copy of the Software in accordance with the end user license agreement that accompanied the Licensed Product. If You are not a licensee of any of the Licensed Products, You may only install and use one (1) copy of the Software for the sole purpose of viewing and printing copies of static documents, text and images created with the Software; You cannot make any other use of the Software whatsoever.
Where's the manual?
The main problem with OWC is its lack of documentation. Once you've digested the 4GuysFromRolla.com tutorial and printed this OWC object model diagram then you're left to muddle around Microsoft's inadequate help files and to ask in desperation at the OWC newsgroup. Don't worry, though. Once you've got started it's relatively straightforward. Essentially, any chart that you can produce in Excel can be generated programatically via OWC. I found useful ideas about what to aim for from the online chart chapter of O'Reilly's Excel 2000 in a Nutshell.
Series ordering
One problem that did have me stumped for a while was how to decouple the legend label order from the series order. If you examine the screenshot on the right you'll see that the legend has the years from 2004 in the top left to 2007 at the bottom right. In the chart itself you can see that the series corresponding to 2004 is at the top, and 2007 at the bottom. Because this is a bar chart, or more specifically a ChartChartTypeEnum.chChartTypeBarClustered, the default series ordering in the chart has 2004 appearing lower, closer to the chart origin. Simply reversing the series order in the data would then make it appear in the wrong order in the legend. After much searching, I found the magic switch was:chart.Axes[0].Scaling.Orientation = ChartScaleOrientationEnum.chScaleOrientationMaxMin;Wrapping up
Before you go out to build OWC into your new Facebook competitor, you should have a read of Microsoft's warning of Limitations of Office Web Components when used server-side. With extensive use of ASP.NET caching I haven't had any problems.
If you need to do charting in ASP.NET (ie. on IIS) then your first thought should be OWC. Despite the fact that Microsoft have decided to stop developing updates to OWC beyond Microsoft Office 2003 Web Components (OWC11) what they have released is , despite its inadequate documentation, useful and complete.