Hi Big Blue
I would bet money that your sloooowww Workbook is due to the use of array formulas. I get many clients with the same problem and 99% of the time it's array formulas.
Array formulas are only a very superficial approach to a problem and are normally suggested by people offering nothing more than quick fix solutions.
The Database functions in Excel can be used in place of array formulas in MOST cases. They are designed specifically for working with LARGE amounts of data, something array formulas are no good for. They do take longer to set up and plan, but that's the way it is when doing a spreadsheet correctly. If you go here:
http://www.ozgrid.com/download/default.htm and download: "DFunctionsWithValidation.zip" you will see some uses of these Functions. Normally it requires having hidden rows and/or Columns for your criteria.
You should also use dynamic named ranges for range referencing in most formulas as this also helps a LOT.
http://www.ozgrid.com/Excel/DynamicRanges.htm
Bottom line Big blue is that the planning of a spreasheet is often more time consuming than setting up, when done efficiently.
Do yourself a huge favour and use arrays ONLY to pull out some data, then delete them, or better still avoid them altogether. Take the time to learn Pivot Tables, Database function, Subtotals etc
I do feel for you Big Blue, as I have seen this time and time again. Unfortunately while Q&A forums like this are brilliant, there will always be the odd few that give poor advise.