I would say emphasize the .net in your title. For example, your logo should say "Your Business .Net". You have to because it's the only way to get people to remember your site. On the other hand, you don't have to emphasize the .com of your .com site.
yes, you got it, and another condition is that when you type yourname, the extension of dot com will be filled itself, and lead people to yourname.com. that's bad for dot net.
You might want to consider using the variation of the domain names but still using the dot com as the tld. Try plural or use stop words in front of the name or behind it for example. Stay away from dot net, even domainers are reluctant to buy dot net.
but the one with the extension of dot net have been registered, if you have a change temporarily, that will be costly, and maybe other domains have been also registered.
Simple, register your name as an official Trade Mark both in US and UK and then offer the .com guy $100 to give the com up amicably (let him know that you own the trade mark). If he says no, sue him. Easy as that! Registering a trade mark will cost you some money but if your idea is unique and if you have a business model behind your domain name (I don't mean advice pages with Adsense code, I mean something that sells, something that is worthy of branding and advertising) having a .com directing to your .net will increase your revenue by some 10 - 15%. So, go for it!