As much to say right away, this 2011 version is mainly focused on transparency. This is the big novelty 2D of this version. Transparency everywhere. Transparent hatchings, transparent layers, transparent objects, transparency prints …

For hatching there are more improvements than novelties.
Exit the hatch dialog box, hatch features are now grouped in a tab of the ribbon.
Hatching also changes in real time, ie it is possible to change the origin of the hatch, its angle of rotation and its scale simply by using the handles.
You knew the system variable MIRRTEXT to put the texts in symmetry or not when using the mirror function, and now there will also be MIRRHATCH, to manage the symmetry on the hatchings.
A new command can also be used to send all hatching in the background.

Geometric constraints also evolve.
A new deduced constraint function appears. This option, which activates or deactivates as you would with object snaps, creates automatic constraints when you use drawing or editing functions. A rectangle created with the rectangle command automatically contains parallelism and perpendicular constraints. Another example is that a connection between two lines automatically creates tangency constraints between the lines and the arc of a circle.

The polylines also have some improvements.
Using just the handles, it will be possible to add a vertex to a polyline, to stretch the polyline (handy for rectangles) or to convert a line segment into an arc of a circle.

Another small improvement that is important is that the annotation scales can contain a default custom scale list, which can be used in all drawings. This scale list can be customized from the AutoCAD options.

The functions of the AutoCAD 2010 Subscription Advantage Pack are now integrated into AutoCAD 2011.

As a reminder, there are:
The ability to hide objects.
In the same way you can isolate one or more objects and show visible hidden objects.
The ability to create a new object with the same properties as an existing object (layer, color, line type, etc.).
The ability to select objects that have common properties (same layer, same line type, block with the same name, etc.).

This 2011 version also improves and especially in terms of 3D features.
A new 3D snap option appears, allowing you to separate snaps from 2D objects and 3D objects.
The functions of extrusion, sweeping, revolutions … can use directly edges or faces.
A new tab in the ribbon brings together the surface features.
Some new functions also appear: A transition function between two surfaces
Surface repair function
A surface creation function by edge selection
A surface cutting function with respect to a cutting shape.
A function to create a solid from intersection of surfaces.
Surface analysis tools are also emerging.

AutoCAD 2011 makes it possible to manipulate surfaces much more easily than in previous versions.
Materials management is also improving.

New materials are available and a materials browser makes its appearance.
Another novelty more specialized, the import of clouds of points. Interesting to import reports from 3D scanner.

We will have understood this version 2011 is an evolution more than a revolution.
The new 2D are interesting but not necessarily useful to everyone.
3D users will certainly find more in this version 2011.

Concerning the system requirements:
The configuration does not change much compared to the 2010 version.
AutoCAD 2011 works on Windows XP SP2, Windows Vista or Windows 7, 32 and 64bit versions.
A minimum of 2 Giga of RAM is recommended.

What about the LT version?
The 2D innovations mentioned above appear to be integrated into this LT version, except for the new parametric ones.
The LT version still does not have 3D features.
The new features described above are therefore not included in this LT version.
Since there is a lot of new 3D and not a lot of new 2D, Autodesk had us accustomed in these conditions to add to the LT version functions that until then were reserved for the full version.
This is also the case for this version LT 2011.
Unfortunately no novelties as grandiose as the extraction of data or the parametric but the appearance of the fast dimensioning function that allows to rate several objects at one time.
The freehand drawing feature is also part of this LT 2011 version and the degraded hatching is added to the list of hatch patterns.
AutoCAD 2011 for Free? download here

AutoCAD 2012
AutoCAD 2010