I use Autocad R14 and have done for some while now. I have also used 2000, 2004, and 2006LT lately. The reason i use R14 is that i am most used to it and have it all set up just the way i like it.
The only problem with using an older version of Autocad is that when sending and recieving others drawings you need to use a drawing conveter. This is to enable you to open any drawings that have been developed in a higher version of Autocad. However these can be downloaded for free and are simple to use.
Autocad R14 is great for what i use the package for. Basically i only draw 2D drawings such as arrangement, detail, sales drawings. For these it is great and very simple to use.
The Autocad family of software has new releases nearly every year with so called improvements and it can get costly to keep up to date with the latest version.
The best thing to do if you are thinkning of using autocad is to simply buy a Autocad Lite package as they are cheaper and do not have so many functions, but they do enough for you to do most drawings.
Once you have set up your Autocad menu's and settings as you like them it is very hard to get used to another version as you keep going to the same place for the same functions. It takes time to set up the new version again as you like it and get used to it. Something that when you are producing drawings you simply do not have (time that is). Well i certainly don't have the time.
Autocad R14 allows you to work in windows, where as most older versions of Autocad did not allow you to work in windows. They only worked in MS dos and therefore could not work on any other windows based programes at the same time.
I find Autocad 2000 just as simple to use and i am sure that the latest version will be just as easy with some more functions available but for the moment i use R14 for most of my drawings.
You can buy the latest Autocad 2009 LT version for around £850.00 were as the Latest full version of Autocad 2009 full version is around £2,500.00. Those prices are for a single version of the programe for a single user.
AutoCAD is used in many industrials for alls sorts of types drawings. I mainly use it for Steelwork detail drawings and then the arrangement. Also used for detailed fabrication drawings, parts details, addembly drawings of mechanical handling equipment.
It is a great package for you does not matter if you are using it from basic simple drawings or for very complicated arrangement drawings AutoCAD is a market leader and is well trusted.
The whole idea is to draw the item/items you are detailing at a one to one scale and the dimension it up so it can be made using the drawing. Also drawings as drawn at one to one scale means that they can be used to produce programes for CNC Machinery to save the need for redrawing.
Drawings are often exchanged using the DXF format between all sorts of drawing packages. Also you can export the drawing as a WMF format to allow it to be inserted into a office based document.
All in all it is a very usefull and interesting drawing package that is a market leader.