I've been using Oneric since the first beta version, and I'm using it on my Acer 5810TG laptop. Recently, though I don't know which day exactly, after performing routine updates from legit PPAs, Ubuntu started with Unity 2D only. Even if I pick "Ubuntu" or "User defined session" on the login screen, Unity-2D loads.
I have built-in Intel graphics which always worked fine with Unity 3D, both on early versions of oneric and on natty.
Please suggest any possible reasons and/or ways to fix this.