We initially bought just the XtraTreelist component from DevExpress, but have been so impressed that we went onto buying the Professional Winforms Suite, and this year we upgraded onto the Enterprise Suite (which does both Winforms and Web).
As a bonus, it comes with code rush and Refactor, which once you get the hang of them, they help save time (plus, it makes your code look pretty...).
I'd say their support is pretty good - I've found a couple of bugs in the past which I've had a reply to within 24 hours, which states they will fix the issue in the next release.
One gotcha (if you could call it that) is that most of their components have a 'Properties' property which is where a lot of common properties get set. I find that a little annoying to use because they need a few more clicks or keypresses to get to, but at least you can get the job done (they tend to put things like input masks in here - regex, numerical etc).
One think that took a bit of getting used to is with the XtraGrid and Treelist, which if you want to do some custom display for specific cells, you have to hook up an event that fires before the cell is displayed.
Hope my ramblings help.
Edit: One thing I meant to add is that Dev Express are rolling out Silverlight and WPF controls too. They're in beta, but you get access to the betas on the Enterprise Suite (I'm not sure about the others). Currently they have a Silverlight Datagrid, a WPF Datagrid, and WPF charts, but they're doing more eventually. In addition, they are constantly adding features to their current products. For example, last month they added Gauges to the controls.