There are some homeless people around, though they usually stay out of your way. Parking can be difficult on weekend evenings if you don't have a garage space. Rent prices are higher than other Mission locations.
Hi, I'm from NY but know the Castro pretty well. it is centrally lolcated and walking distance to many things. I would drive around and get a feel for the area. There is a large homeless poulation but it gives the area some character.
I would agree with Julie that the biggest con is probably the parking. It is a slightly more expensive place to live mostly because of its desirability. But speaking as a current very happy resident and realtor in Castro, the pro's outweigh the cons at 100:1.