From time to time I hear advice that "redirection is bad for your SE ranking". Could someone with the facts please clarify what kinds of redirection are going to hurt a site? Does Google knock you down a notch every time it gets a 301 on your site? Or is the problem that a half dozen URLs pointing to the same content are going to be penalized for duplicate content? (If so, what happens when you "park" a domain as an alias for another?) If a redirection from a given URL to your site goes to a unique site or path (one-to-one), is there any problem?

What I'd like to do is one-to-one redirection on my site to make maintenance easier. A unique and fixed  external name (possibly in "SEF" format) will be rewritten to some other path, which could change from time to time. The idea is that I can change which directory subtree has my production code, test code, etc. without having to copy  everything over from "test/" to "production/".

While I'm at it, I'm thinking about "hiding" the technology by omitting file extensions (so I can change from .php to .jsp to .aspx to... without invalidating bookmarks and SE listings). Are there any penalties for doing this too? I know that it doesn't provide much in the way of security to change every extension to, say, .html, but the intent is to avoid invalidating bookmarks/favorites and hard-won SE listings should I ever change platforms.

There are now few bloggers and marketers that use SEO to help you promote your website and business. And it is also known as the best form of online advertising.