I run WordPress 1.2 and I customised the index.php file and the wp-layout.css file to make it look exactly the way I wanted it to look. I'm quite happy with the result.
I wonder however if much of these edited files are of any use when I upgrade to a new version of WordPress. Will the stylesheet still be usefull after I install a new version? I realise that most likely the changes I made to the index.php file will be lost. However, I can live with that as they are only small edits that can easily be redone. Redoing the stylesheet will be much more of a problem though (and off course very time consuming).
What are peoples experiences from previous upgrades? Maybe there are some users who have been trying an upgrade from WordPress 1.2 to the Beta of 1.3, and who have experience with porting their stylesheet. Did this give you any special problem?