What do these texts have in common?
"Looks like when you're on Google Reader and click a feed that leads to an external page, it now opens within Google Reader as opposed to opening in a new window. Not sure if this feature was rolled out for everyone or if it's still in testing. It opens up in a 'Preview' pane and you can click a button to open other posts up in Google Reader as well." (The Army of Gnomes)
"I opened my Gmail to find quite the surprise this morning – there's now a Feeds link the in the left nav, and reader opens up into the mail space. It's a little awkward, but pretty cool." (mail from a reader)
"Maybe we missed it but gmail.com has a new feature that was unanticipated. When you right click on a gmail email, you get a preview of the email. Just one more way to view all of that wonderful email." (NoHeat)
All the three texts talk about what seem to be new features in Gmail and Google Reader. The new features are actually introduced by Greasemonkey scripts or extensions, but people sometimes forget they installed them. Since the add-ons directly modify web pages, you'll see something else than most other people.