A great number of people, including myself, have noticed that Steam is a wee bit laggy today. And by a "wee bit" I mean it's borderline unusable. Fortunately, some users have found a workaround fix for the issue.

Comments on Reddit and the Steam Community provided a few fixes for this issue that may help you out.

  1. One potential fix is to clear the browser cache within Steam. You can do this by going to your Steam Settings > Web Browser > Delete Web Browser Cache. Please note that if you do this one, the issue will return the next time you start up Steam, at least until Valve addresses this issue.
  2. Another potential fix is to kill off the steamwebhelper.exe process. I would perhaps advise against using this one unless you know what you're doing.

It was speculated that this issue came about from a new Nvidia driver update today. This is not the case. I, and many others, have not yet updated to the latest Nvidia driver yet. This is very much an issue with Steam at the moment.