Pros
Some very smart people work there (although people who've stayed 4 years or longer definitely seem to be leaving and others may soon leave as well after they've stayed long enough for their RSUs). Free chips, candies and sodas on each floor. Pretty flexible work hours and some people spend a lot of time working at home.
Cons
I worked in software engineering and I really wouldn't recommend it to other new grads/college students. Most of the work revolves around very specialized tools/technologies mostly used only at Arista and unless you plan to specialize in working on datacenter switches, there isn't much to be learned that would be useful for school/working at other companies. The projects that they assign to interns are generally a bit trivial/tedious and seem a bit more like extended tutorials aimed at getting you familiarized with the technologies at Arista, particularly TACC, which is the obscure framework that most of their code is written in and takes a while to get used to. A lot of the work also requires in-depth knowledge of the specialized hardware/network protocols found in datacenter switches, and unfortunately there's very little training/resources for learning any of this, although this probably wasn't a problem for more senior Arista engineers, who tend to be from Cisco. On the whole, I was pretty disappointed with the whole experience: I got no exposure to any new languages/tools used outside of Arista and didn't learn any computer science outside of a few obscure networking protocols and features found mostly in Arista's products. Additionally, the offer and compensation are very average and you will likely find more competitive pay at many other companies. During the summer, the internship program also seemed pretty disorganized and important events like intern presentations were barely mentioned/scheduled until the last minute. Interestingly, the company doesn't seem to use recruiters or have HR interact much with interns, but instead just assigns a few engineers the side job of setting up and conducting interviews, as well as sending offer letters (usually sent immediately after the 1-hr phone interview) and coordinating the details of the internship. The fact that these people were also busy working full time on technical problems probably explains why it sometimes seemed like nobody was really managing the intern program and events seemed hastily planned and disorganized. There were a few sporadic intern events that were all a bit disappointing (hiking in a park, watching a dvd in the cafeteria after work, etc.), especially considering that Arista had just had its IPO, although the company has apparently always been fairly cheap especially with regards to perks and compensation. In general, the people at the company didn't seem particularly social or friendly and the office culture and environment overall seemed a bit drab, which made working there feel even more boring as a result. While the work hours are flexible, it seems that the workload is still very high and a lot of people seem to just take their work home at the end of the day and it is pretty common to see/receive their work-related emails very late at night (sometimes 1-2am). There is also a cafeteria on the first floor, although on some days the food quality wasn't very good and unfortunately there were very few other places to eat within walking distance.