At past b2b software and services companies - my experience is a noticeable drop in 'kicking the tires' inbound traffic. For the reasons mentioned, December is not the month people typically start investigating solutions, asking for information, or starting trials. (Many companies hold non-critical hiring until Jan for similar reasons)
Two bright spots to focus on:
1. Any inquiries right now are 'buyers' (like people that visit a car dealership in the rain). Pay extra attention to inbound inquiries this month, they have a pressing need and may be able to convert to sale quickly.
2. Good time to close on existing prospects - offer extra end of year incentive to any folks on the cusp of closing, in some cases as mentioned they have budget to spend or lose, in other cases, you just need to make it worth their while to spend time on you this month rather than next. Don't over-sell, just a get the offer out, wish happy holidays, and either close or move on.