There are tweet ads, yes. They are usually marked as "promoted"
I found it useful to "report as spam" the account they were coming from so at least you only see them once...
I found the new layout to be headache inducing for my english-speaking, left-to right-reading brain so I switched to the Chrome plug-in Silverbird on TVGugs recommendation... and haven't seen the promoted tweets since. Maybe that's because I'm using lists more... but it solved a lot of problems for me.
Anybody else using the beta for Windows Media Player 11? I like it, but can't seem to find an option to have it NOT display the album art, or to merge different songs by one artist into one list, instead of broken down by the album it came from.