There is a lot of discussion out there about diffusion lines, such as Marc by Marc Jacobs, Armani spin offs, or the Go International collaborations available through Target. The pros of having diffusion lines available are that pieces by highly respected designers are made available to consumers trying to live within their means. The cons are that some diffusion lines are made by design teams instead of the lead designer (this can mean the line has little in common with the runway line), thus the consumer is not getting what they are paying for; the quality can be poor, and often the sizing can be difficult to predict.
Personally, I've enjoyed the spoils of the Go International collaborations. Here are two examples of pieces I've gotten this year: