I have a love/hate relationship with SF after living here for many many years since 2000.
I'm from NYC originally (and finally back) and here are my thoughts after shuttling back and forth for many years.
PROS
1. It's probably the safest, relatively big (~ 1M) city that I've ever been to. And I've traveled a lot throughout US and the world. If something bad happens to you in SF, you've really, really should hone your street smarts. And no, Tenderloin is not dangerous at all as I've lived a couple of blocks from there for few years.
2. Probably the only other city (NYC is the other) where you truly have a diverse selection of food. That's pretty impressive for such a small city.
3. It's probably one of the most beautiful cities I've ever been to. I love the rolling hills and some great views especially of GG bridge and Bay Bridge. I wanted to move to SF for a long time, and it took a while for me to sink in that I was actually living in SF.
CONS
1. It's a city of wannabes. Basically everyone lives in the future (they "wanna/hoping to" have a startup, or "do art" etc). Ambitious people are good, but I feel SF definitely goes a bit far in this regard. For startups, it's due to the availability of venture capital in the city, where you don't need to be profitable from day one. In comparison, New York is about hustling and making money FROM DAY 1, not tomorrow, not in few years.
2. The bohemian/alternative/smug feel of the city. South Park had a funny episode about this. For example, people drive Prius in order to "show off" how green and environmentally friendly they are. Some of my good friends (non hipsters or art people, etc) only eat organic and only shop at Trader's Joe or Whole Foods. Apparently Safeway is not good enough. Organic is good, but try going to a restaurant with someone who is stubbornly organic about food content there, and will refuse to go. I mean come on, you're not gonna die if you eat non-organic once in a while!!
3. It's too laid back. If you love New York or East Coast in general, I think you'll find the slowed pace of the city irritating. In some ways this is a consequence of (1).
4. Nobody grows up in the city. This is a big one. I've seen some girls who are 35 and still wear clothing that a early 20s girl would wear. Same for guys. You can be 40+ or 50 and still live with roommates, etc. I've always felt that a cutoff for living with roommates is like 30 or maybe even early 30s, but 40+ is a bit too much.
5. The weather plain sucks. You have windy/sunny-turning-to-foggy weather (65-55F) pretty much all year except about 2-3 times a year when a heatwave (75F+) lasting about 3-4 days comes in and you can finally walk around with a t-shirt at night. There's really two seasons: dry and wet. I respect East Coast's weather much more because I know that in June I will be rocking a t-shirt all day and night and don't need to carry a jacket "just in case". Mark Twain said the coldest winter he'd ever been to was a summer in SF. SF's summer months are typically the coldest in the whole country.
6. Don't get me started on dating. As a guy, I still stick to my theory that it's probably one of the WORST cities to hook up I've ever been to. Most of the places are just full of guys which makes sense since West Coast has statistically more single guys than single girls. East Coast is a bit better in this regard. I always told myself if ever I move back, and that's a big if, I'll have to be married or have a serious girlfriend. And if you're a girl, don't get too excited; I've been told from female friends of mine that the guys are no prize either.
7. Pretentious Hipsters. Need I say more?