First off let me point out that I am not an AutoCAD user...just a lowly project manager who has a project to upgrade some ACAD users to 2011 Mechanical, but will have other users on older versions: 2005 & R14.  The 05 & R14 users will need to be able to access and edit drawings created by the 2011 users.  I have several questions that I humbly bring to this forum for answers.

Can the users on older ACAD versions open or edit drawings created in 2011 without the drawing first needing to be saved to the older versions?
Assuming the answer to the above question is...a SAVE AS to previous versions is required...will all of the data, drawing, references, etc. go through some magic transformation and become available in the older versions or does some of it get lost in translation?  If some data or part of the drawing gets lost, is it obvious to the CAD user that there is missing information?
Are there any known problems or issues with newer functionality in 2011 that doesn't translate to older versions?  k...so I know that kinda sounds like a stupid question because the older versions don't have the new functionality of 2011...what I'm trying to ask in general is...what issues, problems, or missing information will the 05 and r14 users have when they go to view or edit drawings that were created in 2011?
Thank you!  I can now sit back with confidence knowing that I will soon receive answers direct from the experts!

Your 2011 files will need to be saved down to an earlier format in order to be opened on the older versions.But even though the new files can be opened on the older versions, you will most likely experience problems if your 2011 version is Autocad Mechanical and your older versions are just plain Autocad. Vertical products such as Autocad Mechanical make use of special components that Autocad cannot deal with. You can download and install object enablers that will allow Autocad to see the components, but they will not be editable. And since you have to save all the way down to R14, you may end up losing some objects that may not be able to be converted. This is just a guess since I have no way of testing this theory. You could probably explode the components and then be able to edit them in the older versions, but this will make them useless back in 2011 since their functionality will have been removed by the explosion.My advice would be to upgrade your users and get everyone on Autocad Mechanical. I realize this may be a very expensive proposition, but you may have problems if you don't.