"If a 2000 file is opened and any changes are made with 2004/2005, the file is no longer usable by earlier versions".
????? Of course it is. The guys in our office, all have 2004 except me. I am using 2002 still. In 2004, I have set everyone's comp to save as a 2000 dwg. so that I can access it.
When a 2004-5 dwg is saved normally as a 2004-5, it takes up roughly half as much space as it used to in 2002. This is one benefit. The other benefits of 2004, from what I can tell is mostly things like much broader control over x-refs, and viewported dwg's. The "undo" command has been exploited rather nicely also...you can thumb through previous commands and undo the one you choose, without having to go chronologically.
In any case (and I think I'll make this a topic unto itself) AutoDesk is simply driving the drawing industry CRAZY with upgrade after upgrade! It's costing companies small fortunes obtain the new software and the licensing. Does anyone remember R13? Loaded with bugs because it was the first step to operate on the windows OS. R14 debugged the system and everything was great for a long time. It took a while to get around to 2000, and it wasn't what it was cracked up to be. I know the world needs to advance, but most bosses do not realize they don't need to upgrade every single time a newer version comes out. In some cases it renders older drawings inaccessible. Our older dwgs are R14 and cannot be accessed by 2004. Thank God I still have 2002 on my machine so I can convert them.
Back to the point, I am using 2002 and it works great for me. The layout tabs are wonderful. I see no reason to change at this point, and being the senior drafter of so many years, no one else using 2004 in our office can come close to passing me just because of an upgrade.