Although the weather or holidays may exacerbate long delivery times a bit, I've noticed delivery times increasing for at least a year here in the St. Louis area, especially during the last four months. The weather was fine and holidays were far away, so poor logistics and a lack of competitive pressure seem more likely to me.

It's particularly frustrating because delivery for things I need quickly (for example, a PoE switch to replace one that failed) almost always takes nearly a week now, while they offer to deliver non-urgent things (such as Post-It Notes) the next day, if not overnight.