As a top-ranked public school, Cal does draw certain archetypes. Almost everyone here is very academically driven. Finding "slackers" in your classes is very rare, but you will not necessarily be intimidated by the students who raise their hands and comment in lecture. Do not confuse the term "academically driven" with "intelligent" or "wise". Students generally fit either into the category of "naturally gifted" or "hardworking", and while both succeed, it is obviously easier for one than the other.
On a daily basis, the students dress much better than they do at, say, UC Davis, or even here when my sister was at Cal 5 years ago. There is a greater emphasis on self expression and, despite being from the area, I have never seen such liberal accessorizing anywhere else. While you can get away with wearing pretty much anything here (see: shirtless, shoeless), there is something of a uniform. Hundreds of girls roam the campus in knee-high riding boots, skinny jeans, and wool coats in the winter time. Every classroom has at least a half-dozen plaid shirts in it and every other one of those plaid shirts is topped by a pair of thick-rimmed retro-wayfarer spectacles. There seem to be fairly diverse and equally distributed financial backgrounds within the student body, and many students are on full rides due to financial "need". If approved, the financial aid here is very generous and those students who benefit from it live far from meager lifestyles.
On the whole, other students tend to be friendly, helpful, and eager to connect on common ground. Depending upon the classes you choose to take, you may be surrounded by impressively well-read and intelligent individuals, or "normal" people. The extremely intelligent ones tend to be quiet listeners, and can be intimidating to approach, but have always been warm once I've introduced myself to them, in my experience.
.Largely because of the diversity, the school itself tries to foster a very open and accepting environment in which students are able to comfortably share their opinions. There are a few drawbacks to this, however. First of all, students are encouraged to speak freely and often. This means that students who have lived very sheltered lives and have very little life experience will nevertheless enthusiastically take up your class time to share their oh-so-valuable opinions with the entire lecture hall...at length. We like to casually refer to this as the "Special Snowflake" complex. Counselors at east-coast universities have exasperatedly referred to them as "teacups" for their fragility. Most professors here awkwardly tolerate or even encourage it, but a precious few will call out the shocked and flushed student by pointing out that there are, in fact, such things as "arbitrary and irrelevant" statements and 'stupid" questions. In any event, these people exist everywhere, but feel more comfortable expressing themselves at Cal than they might at the type of east-coast school that would openly frown upon them and label them "teacups". There will be at least two in every class.
This overly-sensitive mentality also translates to the political scene of the school. Earlier this year the Republican club at Cal staged a very tongue-in-cheek sham bake sale in protest of the proposed consideration of race for financial aid and admission. Berkeley tends to be a hyper politically-correct campus, and the club took a lot of flak for their stunt, particularly because many of the more liberal students misunderstood their message, and were content to if it helped them slam the opposition harder. I would have to say that students at extremely liberal schools like Cal can go so far as to be "belligerently" liberal, banning together in automatic opposition to conservative stances without researching what they are. Personally, I tend to lie on the more liberal side of moderate, but I was deeply disappointed in how under-educated some of the students and faculty that chose to speak out against the Republican club were about the issue. Most of these types of events at Cal, such as the more recent "Occupy Cal" about which homemade videos of alleged police brutality were leaked, receive national media coverage for their controversy, and the media inevitably sides with the liberal majority of students at the school. Needless to say, it is very easy to get caught up in the "mob mentality" with the excitement and energy and gossip on campus during these demonstrations. Should you end up here, I strongly urge you to try to keep a level and objective head and gather as much information on issues as possible before attempting to participate.
For all of these reasons, the very conservative, easily annoyed, or highly judgmental individual might find life at Cal a challenge.