I've already been using ILMerge to merge output from a number of different projects in a solution into a single EXE or DLL for redistribution (or inclusion in other projects). It works fantastically, particularly via an ILMerge NAnt Task.
There are a few tricks, like remembering that Type info includes the assembly name! If you're directly referring to a Type in code, or a .config file, those references MUST CHANGE if that Type is subsequently merged into a 'new' assembly with ILMerge.
That's pretty basic stuff thought. Both
K. Scott Allen: Using MSBuild and ILMerge to Package User Controls For Reuse
David Ebbo : Turning an ascx user control into a redistributable custom control describe another interesting use : packaging up ASCX-type User Controls into redistributable DLLs. Great idea if you find building User Controls with a Design surface to be much easier than programmatically building Server Controls.
Seems like 2.0 has plenty of cool tricks to offer if you can think of them...