I agree with boater. Every child is different, and you really can't force him/her to develop on a certain schedule. And leaving them to suffer in a prone position because the latest research says they have to spend a certain amount of time on their tummies is probably not the right thing to do if you, the mother, don't feel right about it.
My DD is almost 11 months and is not crawling. I also suffered mommy guilt because I didn't give her much tummy time and tended to rescue her as soon as she started fussing. She never liked tummy time and I couldn't stand leaving her in what looked to me like an uncomfortable and helpless position for long.
She began finger-walking in earnest a couple of months ago, and seems to be progressing well. At the advice of my mother, I started sitting her on the floor by herself more frequently (after I got over my fear that she would be bowled over by her big brother) and observed her while I was doing housework. Turns out, she's a bottom-scootcher. She was very pleased with herself when she learned she could work her way over to whatever it was she wanted. She puts both hands on the floor and looks like she's about to get into crawling position, but can't seem to get both knees under her. So she wiggles, pushes and drags herself to where she wants to go. It's amazing how fast and how far she can go like that. Sometimes she'll wind up on her tummy and drag herself across the floor, but she seems quite a bit less happy with this form of locomotion.
At first the finger-walking was very tiring for me, as I seemed to be constantly bending over her, shuffling along at a slow pace for long periods of time. But now she's down to just holding on with one finger (with an iron grip) and toddles along at quite a pace, free arm reaching out for the latest curiosity. Much easier for me, as I can stand up a little straighter while I help her walk. She even stands unassisted for a few seconds at a time, feet flat on the floor. She cruises a bit, becoming more and more confident that she can make her way while holding on to the furniture. Falling....? Hmmm, I'm not sure, but I think she usually falls on her bottom, but I always try to be close at hand to catch her when she's not in her playpen. Our house has some hazards that can't easily be baby-proofed, so I do try to be close by as much as possible to keep her away from danger-spots.
I don't know of anyone else in either DH's family or mine, who skipped crawling. DS crawled for a few weeks and then started cruising, taking his first independent steps shortly after his first birthday. Perhaps DD's bottom-scootching is a form of crawling. In all, I'm not too worried about DD's development, and it sounds like your DS is doing fine, ao411. I think a certain amount of mommy-guilt comes with the territory, though most of it is unfounded.