Traditional science is carried out by experimentation, interpreting the results in respect to the hypothesis, and repeating this until publication. Publication is everything, and as such it's important to keep your research secret, in fear of anyone publish something similar which undermines the opportunity to publish in a high impact journal.
An open science philosophy says that this closed approach slows scientific advancement. Results should be made available as soon as possible, then everyone in the field can benefit from them sooner. There is no delay for peer review and publication.
Why you should participate in open science
A pure motivation is sharing knowledge for knowledge's sake. Other scientists get access to your research faster. This can prevent groups working on overlapping topics, or research that would be invalidated by new results. Both are possible scenarios, given the time between discovery and publication.
There are also more selfish benefits of open science. Scientists are always more than willing to give their opinion. Imagine you discussed on your website a hypothesis about a gene, and you planned to test it by expressing it in E.coli. Then another researcher, reading your site, wrote to tell you that they had tried to the same but had been unable to. This would save you a lot of time by preventing you from repeating the same mistake. This isn't a hypothetical situation though, this is exactly what happened on Rosie Redfield's research blog. This is just one scenario. People willing to tell you a better way to perform an experiment, or alternative interpretations of results are other possible benefits for the researcher willing to publicize their results and ideas early.
Why you should shun open science
There's one very obvious reason for being cautious about making your results public before you publish - will people steal your research for their own benefit? Unfortunately the answer to that is likely to be yes. While we would like to think that everyone would be honest enough to acknowledge your work if they use it, some won't. The nature of the scientific game means that we get points for publishing in important journals, and the more points we get the better the scientist we're regarded as. If someone can increase the significance of their work by repeating your analysis, as their own, then there's always the possibility they might. I don't think we should be surprised at this, since this is the way the system is set up, and until we can come up with a better one this always likely to happen.
There are also other people that have a stake in whether you make your research publicly available. Your work is likely sponsored by a research council or funding body. Your institution gives you a place to carry out your work. Co-researchers contribute time and data to the project. All have something to lose if you're risky with your research, and are scooped. They all may be less willing to work with you as a result.
There is one last point to consider. If you make public a figure that describes your research, that figure may then be ineligible for publication - similarly for conclusions, and interpretation of data. Journals have different policies on what researchers can make available prior to publication. It's worth taking a moment to consider this before putting data on a website.
A middle way
Despite all this I am very in favour of open science, and would like to make all my research available for any one who is interested. However the reasons against are considerable, and should not be ignored. But after speaking to other people in my department, we've come up with a middle way.
There are always experiments that don't work out. The results were inconclusive, I have no idea of how to interpret the results, or the experiment just didn't work. I've got nothing to lose by making this data publicly available, I'm not going anywhere with them anyway. However, that's not to say they might not be useful to someone else, or even better somebody could give me their opinion on where I've gone wrong. I think this could be a good start for my experimentation with open science.