I haven't read the entire thread (Ok, I'll go back and do that!) but just reading to page 2 made me want to reply. I have many, many guy friends. I work with mostly guys and it suits me and DH both just fine.
I have one I'm very close to. I'm his first phone call when something happens in his life (after his DW, of course). We used to work together and, at the time, his DW had a rule that he couldn't spend time alone with me (actually, it was any woman). As she has been around us in social situations and seen our interaction (I'm the first to slap him around when he's done something stupid or isn't treating his DW like he should!), she has removed that rule for me. We've traveled together for work and there has never been any concern at ALL from DH or his DW. She tells me I'm the voice of reason in his life and she likes the additional "female" perspective. We've both changed jobs and we see each other rarely and only talk on the phone about 3-4 times a year (sometimes for less than 5 minutes, just to say hi and check on each other). But he's still one of my best friends.
DH has one female friend who he works with daily and is very close to. They do things together (they are doing a 5K soon, in fact) and I don't even think about it. She'll hang out with us at the house and has been here before when I wasn't. I never even occurred to me to worry about that. She's awesome, actually.
I have, in fact, been burned badly in a relationship where a friendship turned into "more." But I see it this way - if the only way to ensure the loyalty of my partner is to forbid him from having any other friends of the opposite sex... well, I guess that's not a relationship I want to be in. I want to be married to someone who I know has other options and still thinks I'm the best.
