Ubuntu 2D has been dropped in Ubuntu 12.10, which means some low end systems may face occasional lags while using Unity and searching from Dash. Fortunately, there is a work around for those troubles by slow speeds and lags. For this, you need to add the following line in your ~/.xprofile file. If the file doesn't exist, create it.
The line enables low graphics mode in Unity which disables some fancy effects like active blur and transparency.