Pros
Mostly nice people, onsite cafe, office supplies, location, facilities and great IT staff (these guys really go out of their way to help you out). On a side note, I'm glad not to be part of IT, since they're only contacted when something goes awry. Outlook for the firm looks good. There were two layoffs a couple of years back, but work has been steady and busy for the most part. And unless you do something really dumb, chances are, you won't be fired (the first time around).
Cons
You work with attorneys. Some are nice, some are jerks and some intentionally go out of their way to demoralize you. Even the nice ones have their moments. They are all petty to some degree. Coming from two other law firms in SF, I can say that the upstairs/downstairs mentality is much less pronounced here. However, I feel that firm values are changing and Cooley may soon fall into the ranks of Wilson and the like. I know most associates. paralegals, and staff, myself included (obviously), feel under-appreciated and overworked. As a non-exempt employee, I find there is no benefit in working harder than my fellow assistants. Rewards are minimal best and pay seems to be solely based on seniority. No upward mobility, nor do they encourage promoting within, but it's a law firm so that's to be expected.