In the end, a video posted yesterday by Google's Matt Cutts basically summarizes that using either the bold or strong tags don't better affect SEO strategies over the other one.
This is old news. As Matt mentioned in the video, the same question was asked in 2006 and the answer pretty much remains the same - it doesn't matter. What is important to take from this video is that, according to Matt, the bold and/or strong tags indeed do not affect SEO.
From my perspective, I would never say that using either of those tags has helped a page of mine or a client's page rank in the search results. Even if the bold or strong tags were one of the 200+ ranking factors (which they aren't) I truly wouldn't worry about it from an SEO perspective, at all.
The only matter the strong and bold tags come into play in my work, is from a usability perspective, (making the user's experience a good and meaningful one). For accessibility purposes, bold is used for visual presentations and strong equates to emphasis.
Here's a great piece of work that puts the use of bold, em, strong and italic tags in perspective.
If you're a good writer/editor, and you fully understand when to use strong or bold tags, then go ahead and use them. Google's ranking system is so sophisticated that you don't need to, and you won't succeed in doing so, if you are using those tags to rig the system (rank better).
When is a good idea to use bold or strong?
If I'm not going to use a heading tag (i.e. H1, H2, H3) then I will use the strong tag as a substitute. This would be a case where I'd rather simply emphasize a sentence that could or would be considering a heading visually.
Other than cases like these and other grammatical instances, I definitely advise you not to worry about using the bold or strong tags to help improve your rankings. Use them naturally and you'll be much better off with your endeavours.