Google used to love subdomains like http://myporn.pornsites.com/ but due to spammers and the like they have now devalued that type of site setup and have instead made but subdomains and subdirectories very close to equal.
They also used to see subdomains and domains as two different sites and from what I’ve been reading they supposedly are only making smaller sites equal. It seems that larger sites that use subdomains are business as usual so I’d sugget not using subdomains anymore unless your site and subdomain are very large. Yes, as usual, you can do a search and find all kinds of exceptions. However that doesn’t mean they haven’t made the change and that those same sites you find now will be found in the same position in the future. From what I understand it’s going to affect mostly smaller subdomains with few pages. Lol, you got it, The big G views it as spam and a way to manipulate PR.
I must say that I haven’t tested this on my porn sites except for a very long time ago. However I do subscribe to several newsletters who do test things like this and they are people I trust. I’d also include the ‘Google Guy’ Matt Cutts as a source. They all say that now a site in a subdirectory is as good as or even better than a subdomain.
Naturally I put a lot of my non porn things on subdomains. Lol, I suppose I could change them but it would be hard to do with some of them. Wish I’d have known before I set things up the way I did.
Because Google sees domains and subdomains as seperate sites you get more link credit to your main site with a subdirectory than you do with a subdomain.
What I now recommend is using subdirectories rather than subdomains. With the extra juice you get from incoming links you will come out better for site popularity and for PR. Doesn’t matter if you run a non adult site or a porn site.