Hi Scott,
We don't have any particular issues using FIFO at the moment. You can check the Knowledge Base - there are some articles about FIFO. Also, this is from the User Guide on Inventory.
FIFO — The item is valued using the first-in-first-out method. Cost information is retained using cost layers, which is described further in the ―Inventory Costing‖ section.
The FIFO method requires tracking of inventoried items by the order of their respective receipt dates and numbers, along with the associated cost of each addition. When items are removed from inventory, the first, or oldest, in the site is removed first with its associated cost based on the receipt date and number. Since inventory often is removed in quantities different from those added, withdrawals can carry a weighted value, because the withdrawal came from different layers, or receipts. Cost layers will be tracked for transactions associated with an originating transaction.
If you have a specific question on using the FIFO inventory valuation method, we could try and answer it for you.