I've always had a hard time with opera. It requires independent twin I-beam suspension of disbelief to hear Mimi belt out one last aria while dying of TB, you know?
Second Life isn't quite that bad, but it does differ from RL in a lot of ways. Some are good. I'm glad I can fly, and that falling doesn't hurt me, and that I can teleport. I can do without having to eat or sleep or do other tedious physical things in SL. I love having an unbounded closet that doesn't take up any room, even if it's currently disorganized.
Some things still bug me, though. Others strike me as weird. Still others are kind of a bummer, but can be passed over with sufficient motivation.
"We are the hollow men..."
If you zoom in closely enough, you'll see that your avatar is hollow! It's probably not worthwhile to change, but it sure is weird. (Cheyenne did a nice blog entry on this a while back.)
"Whoa... those jeans look painted on..."
In SL, they are. Shirts and blouses, too, so if they come down far enough, it looks like they're vacuum sealed to your posterior. That may give rise to imagined discomfort and very unfortunate mental images, but as far as damage to verisimilitude, it's worst for shirts and blouses. The better endowed you are, the worse the effect... well, if you're interested in realism.
(Actually, that may not be entirely true. I have some jeans that I can put on and then look up the legs... and see that it looks like the jeans were filled with flesh-colored stuff after I put them on, and my ankles and feet stick out from it. I bet they are at least partly prim-based.)
"In one ear and out the other"
SL doesn't always bother with that thing about matter... you know, the bit about no two pieces being able to occupy the same location at the same time? This is useful for building, no doubt, so you can approximate a non-prim shape as the union of overlapping smaller prims, but it can lead to weird results, like having your prim hair go through your body.
Animations, poses, and the non-average man (or woman)
At least so far, animations and poses aren't parametrizable; they're made by someone who's got two particular figures acting it out, and it looks good on them. The more you vary from those figures, the more off the animation looks. In an embrace, you reach up and grab the air above your sweetie's head (if you're tall) or attempt to strangle him or her (if you're a bit short), or you gaze lovingly into your partner's torso (if you're very short, and for purposes of discussion, we will ignore the chorus of "So what's wrong with that?" that might arise). You sit... and if your legs are too long, your feet go underground.
I could believe it's computationally intensive to customize such things on the fly, so one might as well grin and bear it. If you're in an embrace, you're paying attention to other things, anyway... but in a photo, everyone will notice the glitches, darn it.
Don't they sew those skirts up all the way?
Ah, flexi-prim skirts. They look so beautiful... until you sit down. Then you find out just what those "glitchpants" are there for. Or, you start your descent, after fastening your seatbelt and raising your chair to the full upright and locked position... and have your vision blocked by your skirt, which looks like a beautiful if wind-blown flower with your legs as the stem. (And you really discover what glitchpants are there for.) Ah, well. One must simply deal with it... and stand up if someone's taking your picture.
One of these days, SL and graphics technology and processors will improve, and we won't have to ignore things quite as doggedly. Even now, though, it's scary how easy it is to immerse oneself in it, so I can't imagine how hard it might be for some to tear themselves away from it when it gets really good.