Aaron, LOOKUP function requires that the vector or array be sorted. And, you can't tell it to require an exact match. The exact match is critical in most of my lookups, so I stick to the MATCH function.

Sometimes I'll use VLOOKUP for temporary spreadsheets, but never for something that is long lasting. It is too likely that I'll come back a month later, insert a new column, and not notice that I have broken the vlookup functions.