When is the last time you took inventory?

I really wish I knew why this came to me today, but it may be because I haven't taken a thorough inventory in months.
I was at a regional eBay seller convention in Atlanta a few years back. At the time, the biggest concern was eBay hiking the store fees a few months before Christmas. While there, I was talking to a bookseller about a particular graphic novel my wife wanted. He told me that he really didn't have a clue how many books he had, much less what titles he had. I thought, "How can you run a business like this?" Then again, I have done the same thing, on a much smaller scale, since November. The reality is, he told me later he had over 500,000 books. There was almost no possible way for him and his 2 employees to look at every single one. But there was a way for me to count mine.
At the time I was a Gold Powerseller, and had a 12x15 office with two walls completely covered with bookshelves that were slam full of movies and games. There were over 6,000 at the peak of my business, and each bookshelf held 300.
I took my first inventory when there was just one bookshelf with about 150 movies, and found that every one of the movies I had was listed on eBay. Once I reached that 6,000 mark though, it became somewhat more challenging to ensure they were all listed for sale. Using Turbo Lister, I had everything set to just punch in the UPC, add a line to the title of each, and upload. But, sometimes the UPC wouldn't work, and I didn't catch it. Or maybe the Good til cancelled would cancel. Possibly a non-payment that I just forgot to relist. In any event, I always had at least a few each time that weren't listed.
My strategy:
There were really more movies than I could count at the time, so I devised my own strategy. My wife, or the employee I had hired, would call off the names and the number on hand. I would search my eBay store for them. If they weren't in the store, they would go onto their own little shelf to be listed. That took care of any strays that got lost from eBay, but it didn't help me see if I had any listed that weren't actually in stock.
The easiest way for me was by just matching up total counts. I took a total title count and matched with my store, and if I was within 10 of what I had listed on eBay it was going to be a pretty good month. The entire process took about 4 hours a month.
I would count like this once monthly, and do just a total title count mid month, and it worked.

I have known sellers who take elaborate means to calculate, file, and stock their inventory who couldn't keep up as closely as I did, and take twice as long or longer to count. The truth is, when dealing with inventory I have to treat it like cash.
Rule 1: The less I handle it, the better off I am. I can't mess it up if I leave it alone, right? This goes for any product, in any quantity. If I am selling glass products, I am probably going to mishandle them if I touch them enough. If I am selling clothing, I will possibly stain a piece by moving it back and forth, or get so dust on it requiring me to wash it, costing money. The same with movies. I didn't open cases more than necessary, wouldn't move them around too much except to make room for new inventory, and I certainly wouldn't use them!
Rule 2: The simplest method is usually the most effective. I always shifted the movies and condensed them as far as possible, that way my newest stock would always be on certain shelves. I could have setup a spreadsheet with all the UPC's from a Turbo Lister import CSV file, sorted by date uploaded, and walked each shelf to match up all the UPC's or titles. Just setting up this spreadsheet would have been a couple hours, then setting the counting would have been an all day affair. Then, I am stuck counting them all again later! Sure, I would have been 100% accurate, but I would have missed about 20 questions leading to possible sales that day. So I may have missed $50 in inventory, but I would have lost $150 in sales.
Rule 3: Strive for thoroughness, not necessarily 100% accuracy. I never missed much counting with my methods. When I did, I would catch it the following month. The most thorough methods of counting inventory are the most simple, and I lived by that rule.
Rule 4: If it isn't making you money, it isn't always costing you money either. I would keep thousands of movies in stock for a couple months at a time, with sale prices averaging $7 each. My cost was usually 50%, and eBay fees were a nickel for each month. My newest inventory would always be what sold, but when I ran a special for free shipping over $50, my sales of the long term store inventory would skyrocket. In turn, I made much more this way than selling them at cost to re-invest the cashflow. While this doesn't necessarily work for high ticket products, most that cost less than $10 deserve a couple months to sell at full price.
Rule 5: The final rule... Don't take it too seriously. I could not forget I had a strong personal inventory as well to keep in check. I couldn't spend all day counting and barely see my wife, so she would help if possible, then I'd take her to lunch. It was a very simple way of making sure my inventory, while it controlled our finances, did not control our lives.

I still take inventory, although not for a couple months, but I must when dealing with suppliers at least keep an online inventory working. Keep working to perfect your process, and by all means, keep it simple!

Now if you will excuse me, I am about to start counting.