Acrobat 6 was the version w/ the big / slow-loading problem. 7 wasn't too bad at all and v8 loads quite quickly on my 800MHz P3. If one wishes plug-ins can be removed to further speed up pretty much any version.
That said, another interesting alternative is Sumatra PDF:
http://blog.kowalczyk.info/software/...pdf/index.html
which I see has finally gotten auto-reloading of changed .pdfs and pdfsync integration.
William