I've wondered about open office for a while but as an avid user of
excel, I'm curious to know how the OO version compares to M$ Excel which
I find extremely versatile and capable.

Personally I've not Microsoft Office installed on any of my machines for
well over five years, and I produce and receive documents from many
customers, I can think of a few that needed minor tweaking (of the sort
that would happen when changing printer or paper size) but can't think
of any documents that were a write-off.

For your spreadsheets it depends how sophisticated a user you are, for
sheets containing "just" formulae and charts, no problems, it'll read
and write .xls files, when entering new formulae you need to get used to
";" instead of "," I can't speak about "advanced" usage.

If you make use of VBA macros then the stock version of OOo won't play
it has its own scripting instead, but the Novell Version (who signed a
pact with the devil) known as go-oo is available - can't say I've ever
used it

http://www.go-oo.org/download/