Not heavily, no, and definitely not on Android (at least), where they have some algorithm to reflow the timeline both at random times, and after viewing a specific tweet. Click the back button to continue reading your timeline and they insert 5-20 tweets in between the one you just read and the one you were about to read, or they pop you up to the top of your timeline.

It's truly a bizarre UX, and the only charitable way I can interpret it is that they're using Continuous Delivery, implementing features in a piecemeal fashion, using users as alpha testers, and basically moving slow and breaking things.

That's actually one of my concerns. As a heavy Twitter user for like 8 years (I spend at least one hour a day in that app) it is obvious to me that those involved with Twitter do not use the product at all.