I use a 4 workbook system that meets my needs as a 24 year old with no reason to estimate a precise retirement age or portfolio draw down ability at this time. Each workbook is fairly complex in its own right, but as others have said, it was developed by me so I know exactly what is going on. I think the key is to find something that is simple to update going forward and provides you with useful information for decision making - while I spend countless hours analyzing and tweaking my spreadsheets, the actual "required" time to update each is about 1 hour at the end of each quarter.
1) Net Worth Spreadsheet (my "scoreboard") - this is updated quarterly with the balances of all asset and liability accounts and tracks changes to NW quarterly and yearly
2) Asset Allocation Spreadsheet ("benchmarking") - this gets into the detail of all my holdings, from the checking account, to funds within the 401(K). Within this workbook I have my holdings dissected in pretty much every way imaginable: Taxable vs. Tax-Favored Holdings; Total Asset Allocation across and within accounts; Large vs. Mid vs. Small; US vs Int'l, etc, etc. I also update this spreadsheet quarterly.
3) Cash Flow Statement - Here I track my money coming in and my money going out (to expenses and savings). This allows be to forecast how I will handle different scenarios (e.g. raises, debt-paydown, increases to savings, etc.).
4) Budget - pretty standard here, I try to track all expenses by category by month. I am not a huge fan of tracking every single penny, but the DW likes to and I figure in our early years it will give us a good baseline for estimates going forward.