general.tax.pricesinctax - this determines
whether the prices for items you enter in the back end are inclusive of tax or not. In the US, prices would typically be entered exclusive of tax, and this setting would be 'n'. In Europe, it is more common that prices would be inclusive of tax (though business-to-business oriented sites may use ex-tax pricing).
frontend.users.access - this provides control over the level of access to the site that the public has. 'No' = full site viewable 'Yes' = must login to view site 'Partial' = prices & add buttons hidden until login 'Browse' = full site viewable, must login to checkout
frontend.display.images.large.linktype - this determines whether large views of images are launched in a new browser window [n] or within an ajax popup [a]. The latter is generally preferred these days as it's virtually instant and also avoids some of the issues with popup blockers that may interfer with launching new windows depending on browser settings.