How long does the google penaly last?

I'm not Matt Cutts but I suppose that as long as you remove the offending trigger, you should do fine.

Sometimes Google gives a penalty to check if the website is following the whitehat process or not. And they will monitor the website very closely. If you do anything out of box, it will not help.

But do what you are doing (if you are confident they are whitehat) and it will be the proper way to negotiate Google penalty.

I am not sure what you mean white hat way to recover "other than" guest blogging, blog comments ect. If you are looking for a magic formula, other than creating great content, guest blogging, videos, etc, you are probably not looking at anything that is going to be considered "white hat". You want to create great content, and then have others share it and link to it through social networking, etc.

Anything artificial is against Google's terms of service. In fact, really anything promotional is. I am not sure of the reason for your penalties, but first, make sure your site meets the guidelines spelled out by Google.

Make sure that you remove any links out to bad neighborhoods (Link farms and blog networks, etc). If you are seeing a penalty, there is a good chance that this is the culprit. While Matt Cutts no longer says it is "impossible" for inbound links to actually harm your site, he does say that they try to make it "difficult. If possible, remove any spammy inbound links, but like I said, the culprit is more likely to be your outbound links than your inbound ones.

Are you sure that you actually have a "penalty", or is it actually that most (or all) of your inbound links were considered artificial and unreliable, so Google just discounted them? Not that they actually gave you a penalty.

Finally submit a reconsideration request to Google. I think getting your site into compliance is more important than "waiting" out a penalty to expire.

I have heard and read but I cannot remember where that penalties can last at least 6 months, but I have also heard of folks having trouble with their sites even after a year and is the reason that some choose to rebuild their sites and redirect them to a clean domain.

It is only penalised for certain keywords it seems. The site is definately penalized, as the competition is low for this keyword. I am an ex-bmr user but my other sites have not moved and one of those I really hammered with bmr.

There is not a certain period to pass Google penalty. But posting unique content to your website and making powerful backlinks form any authority website you know, helps your website to pass this problem faster. Google penalty usually happens because of these two problems and you need to solve them to overcome it.

If your site is de-indexed then the penalty is likely permanent. If it is just rank changes then just need to build more links and get more unique contents to the site, it will bounce back easily.

It's not de-indexed. Does the unique content have to be on the home page or can I add sub pages and still get the desired effect.