If you can't get the perma-link structure of wordpress to match as many of the old pages as possible then, yes, I would personally 301 the old pages to the new ones.

You'll lose a certain amount of "link juice" by doing this, but it's better than losing it all!

What does the forum think the best strategy for social bookmarking is?

Obviously white hat, user generated would be preferable but looking slightly darker; you can obviously get services that create social bookmarks over a period of several weeks, but are they worth the investment?

Google uses WHOIS to determine the age of the domain under a current ownership, however if the WHOIS data changes and at the same time the content of the site changes dramatically, Google may reset the domain age of the site in their opinion.

I'm not sure but I would imagine Google have their own records on domain age outside of WHOIS registration.

Vjay - good question

I think it really depends on the quality of the directory. I think that relevant (industry specific) directories are generally ok as long as they are high quality and not rife with spam.

There are also some credible directories still such as yahoo directory, best of the web, etc. So if you can find a decent one with decent inbound links and a solid auditing process, then why not.