Interesting how this thread revolves a lot around "adventures in becoming not single" and gratitude of not having to participate in said exploits.
How about the experience of actually living a single life?
I've been "single" for the past ~19 years (dated some during that time, but nothing serious), and I'm only 40 right now. I've been fortunate to have a good friend who is also single to do stuff with (including travel) for most of that time, but I still do many things on my own.
I've done the online dating thing, the go to bars/clubs thing, the "just try to meet people where you do stuff anyway" thing, the "keep it casual thing, and the "don't look for it" thing. At this point, I rarely even think about trying to date anymore (every couple years I'll log on to one of the dating sites and update/activate a dating profile, but rarely does anything come of it).
So, to answer your question, what's life like as a perpetually single guy? Pretty darn enjoyable most of the time. It's a lot cheaper when I'm not dating someone (even dinner and a movie type dates once a week can add up quickly!), I'm practically guaranteed to enjoy all the activities I do (as I'm the only one I need to consult when deciding what to do!), I have multiple good friendships and close family on top of a decent sized network of other friends/acquaintances to socialize with when I want to, and I can choose to stay in when I feel like it or go out when that's what I want to do. I enjoy setting my priorities and never feeling the need to compromise what I want in order to accommodate someone else.
I still vaguely remember what being in a serious relationship was like during the good times (my last serious relationship included living with my then GF for ~9 months), but almost never miss the positive things about a serious relationship that I don't get since I'm not in one. Maybe "loneliness" will be a larger issue when my dog eventually passes and I'm actually going to an empty house (some have suggested that might be the case before), but for now I probably feel "lonely" less often than many married people. Sex isn't nearly as frequent as I'd prefer most of the time, but if I really want to get laid that isn't too hard to accomplish. The rare time when I want to go do something (like travel) and no friends are available to go, I tend to wish I had someone who could accompany me but I've always managed to enjoy such occasions anyway.