I've used DevExpress for WinForms applications, mainly for the XtraGrid.
However the rich functionality comes at a cost:
your development team has to learn and embrace the sometimes complex design.
some things just don't work properly, and you need horrible hacks to work around limitations. Fortunately DevExpress support is usually very responsive in providing solutions and workarounds.
some things don't work at all - e.g. the XtraGrid does not properly support saving data from a grid row-by-row.
the licensing is quite limiting: to install a licensed copy on a development machine requires a connection to DevExpress's server; I don't know what will happen if DevExpress ever go the way of Lehman brothers. In mitigation, a source code license is reasonably priced.
Broadly speaking I'm happy with the choice. But I would want to do an in-depth evaluation of the competition (e.g. Infragistics) before making a recommendation.
