I've have worked with lots of systems that utilize the 1 table approach to lookups. And my opinion is that they should never, ever be used. Imagine making a datawarehouse that relies on loopups for values. Analysis services will not allow complex joins with where statements, so you will need to make views that combine all the data. Now take the main table (say a list of employees) and say you need to return 18 different lookup values. With 1 lookup table structure your where statement is huge and unless well indexed, the joins will perform terribly.

Anyone that has ever done analysis on data from a system with 1 lookup table will tell you that it is a bad design and difficult to work with.

Now think of table size for your 1 lookup table to work you need an extra field to store what field the value is used for. Suppose you have 500 lookup values, you could create another table for values and maybe only store an int for the field value, but then you need to do another join to figure your values out. Anyway having 1 lookup table will take up more physical space regardless of the design.