Pete,
Did you decide that Draw looks like Powerpoint, which you already have, so you didn't really need it? Most of the OpenOffice programs look very similar to their Microsoft Office counterparts. They were designed that way so the transition would be easier. In fact, OpenOffice will read in MS Office files (Word, Excel, etc.) and will also output in those formats if you choose.
But even though the OpenOffice programs look similar to the MS Office programs, they have some advantages. In the case of OpenOffice Draw, the advantages over Powerpoint for map drawing include:
1) It's free. And it has been available for free since 2002, so that's not likely to change. Even if you already have MS Office, you'll still need to pay for the next version.
2) It has layers, which makes it easy to use a background map as a guide.
3) It has much better control over line thickness and text size and text manipulation.
4) It will export to PDF format.