Like most larger cities in the US, Berkeley has some areas that are worse than others. The area on the opposite side of the interstate from the marina seems to be one of those areas. I have also heard that People's Park can get bad especially after dark.
While it's possible you may read about People's Park in the history section of some guide book, it's highly unlikely that any will suggest that you actually go there. And with good reason.
People's Park was the epicenter of many free speech protests during the heyday of the movement back in the 60's, but today it is little more than a homeless toilet. There is absolutely no reason why you should go anywhere near it, though you may stumble across it if you do some shopping on Telegraph. Far from being a place of inspiration, it is a very dirty and depressing place. If you want proof that the 60's are dead (or, at least, not at all well), visit here.
Lots of unsavory folks hang out around here and it should definitely be avoided at night.
It is located on Haste St. a block east of Telegraph.
Avoid Gilman Street exit off of Interstate 80 highway as much as possible. There are no stop lights at the intersection, and vehicles on Gilman street have the right of way in this 6-way stop. The traffic is a total chaos at most times. Take Albany exit then go to San Pablo ave as an alternative when you want to visit the hip 4th street shopping district.
I wouldn't characterize Berkeley as a dangerous town, but if you aren't careful about your surroundings you can become a victim. Cars get broken into, purses get snatched, I've seen a bum running down the street with a TV, and even know a couple of people that were held up at gun point. The usual stuff are limited to petty crimes, so I'd never walk around with alot of money in hand at night. Check out the University police crime alerts website: http://public-safety.berkeley.edu/police/crimealerts.html
One of the things that most people are caught off gourd with Berkeley is the amount of young transients that take refuge here. With the cities liberal attitude and mild climate, it has been that way, as long as I remember it.
Also, not to say there is a connection, but petty crimes like car being broken into is prevalent.
Like other East Bay cities, Berkeley has some dodgy areas. Most of our innumerable homeless are harmless and quite friendly, but there are occasional instances of petty crime and mugging, especially in the area around People's Park. I recommend avoiding this area at night altogether, unless you're in a very large group. Also avoid any area at night where there's a liquor store on every corner (common sense, right?). Despite the Berkeley City Council's good intentions, there remain many depressed areas of the city, and crime statistics can be alarming.
At various places in Berkeley and the area attractions you may see warning signs. These are there for a reason, usually your safety and to preserve the area for future visitors. Please obey them.
Although a symbol of the Free Speech Movement in the 1960’s, the area is now a haven for the homeless and drug dealers. Don’t hang out here, especially at night!