Yes, you're right - OpenOffice is significantly slower and more resource hungry than MSOffice, see
http://blogs.zdnet.com/Ou/?p=120 - and -
http://blogs.zdnet.com/Ou/?p=119
You get what you pay for (or rather, don't pay for). OTOH, OpenOffice is evolving very fast and improving speed is high on the developers priority list. Several revisions will appear this year and by the time OOo 3.0 appears much of this should have been remedied.
The troubles interpreting MSOffice files are hardly OOo's fault - the Microsoft data formats are secret and OOo has to black-box reverse engineer them. It's amazing that they have achieved the level of compatibility that they do have. Simpler documents do not have these problems - I don't normally read or create complex documents and have no problems.
"....I shall leave it on for a while and play..." seems like a good plan.