I started drawing vectorial in 1992 with Corel Draw. Soon the next releases became bigger and bigger, but the software grew unstable and uncomfortable for the designer who doesn't need cliparts or a nice interface, but need solid import/export and trans-format copy&paste, or a quickly adjustable grid system.
So I quitted Corel Draw for Designer, but this software became heavier too.
Plus, you can't dream of working on both dxf, cdr and ai in a team using both Windows and MacOS and Linux without having importation troubles.
The solution is the open file format SVG and its main and most complete editing software: Inkscape.
I use Inkscape since 2005 and followed its releases until now. I think the latest releases are stable and fast.
Lately, a few weeks ago, I found that you can easily edit a isometric world with this fantastic software, and there is plenty of tutorials about the way to do this:
AhNinniah's Isometric projection in Inkscape
Inkscape's Creating Isometric art in Inkscape
Tuts+: Play with isometric projection
I used the last one to setup the grid in Inkscape, for editing the levels in DumDum.
Extremely recommended.