If you are tired of that extra Steam sales dialog box that spits in your face every time you start the program, you can disable it. To do so, go to your settings via Steam -> Settings.
In the dialog box, click on "Interface" and uncheck "Notify me about additions or changes to my games, new releases, and upcoming releases." Here's a picture of that dialog box and option.
Q: You know you can turn that off right...? A: No. No I did not.