This is likely to be either a browser or connectivity issue. This is to let you know that I am using Firfefox 10 and I can view the youtube in this post > Enjoying a “Breezy” ride.
How are you connecting to the internet and to WordPress.com? The way you connect to the internet (mobile, satellite, DSL, dial-up) and to your blog, and how many proxy server jumps etc. it takes to connect can cause problems. There maybe be problems with your ISP and/or with the proxy servers.
If clearing your browser cahe and cookies does not work for you and you have an outdated browser version you can upgrade it here.
Exactly which browser and version of it are you using? And do you have another browser that you can try?