I stayed at
this place when I was out there a couple of years ago. It's a bit outside of the city, but is super chill and has rad views of the mountains. The trains out there stop earlyish, but I think there are still night busses that you can take back...so not the best place if you're looking to hit the bars or skate all night, but great if you want to skate all day and chill at night. They have a kitchen so you can make your own food to save $$, and a patio you can chill on till 11pm or so.
For skating: I had the raddest times just cruising around, finding spots. Sants sucks now, you can only really skate MACBA after 6-7pm (though it's still cool as a warm-up spot)...my favorite times were just cruising around, meeting some dude from a random country, and skating around together finding spots and shredding. All the skaters there are super friendly and awesome...the raddest culture. I saw people pickpocketed a couple of times on the subway, but if you know how to keep your shit together in a typical city, you're fine. Just don't be stupid and you're good. I ended up going out with my phone in a front pocket, some cash in my jeans' coin pocket (nobody's pickpocketing that shit), and a copy of my passport in a ziploc in my other front pocket. Back pockets are for maps and water bottles and other shit you can lose.
Barcelona is the RADDEST for skating. SF is the only city I've had more fun in.
OH! Also, if you're into tattoos, check out
LTW, in an alley off La Rambla. I got some work done by Javier Rodriguez while I was there, and it's so good. And all the dudes there were super cool.