I use keyword subdomains for one of my sub-sites and it seems to help with my pagerank, etc. But I don't use it very often.
I think it comes down to a personal preference on design. For instance, yahoo has their site setup so you can access many different sections via subdomains. (ie - finance.yahoo.com) It makes it much easy to remember than www.yahoo.com/finance/ in my opinion.
Just be sure which way you want to go, because if you decide down the road to switch, your current pages/search engine rankings will have to be re-indexed with the new page/url format you choose.
Good luck!
But if each of your subdomains has focused and substantial content, you should not run into trouble at all. Many major sites use subdomains - About is one. If you want to study their success in the SERPs you'll see that subdomains can be fine.
The page the video is on is on the main domain, but the content is pulled from the sub-domain. another nice thing about this is that I can put a bandwidth cap on just that one sub-domain and when it reaches it's limit for the month (for my hosting), only that content is not accessible. The rest of the site will function fine.