Pros
Guidewire offers one the opportunity to do something more interesting than just writing TPS reports or another boring data collection web-app. Guidewire is filled with more than your average amount of highly skilled and intelligent people. It may be that every organization says that, but my experience at Guidewire has shown it to be exceptionally true here. It is truly a great feeling to bring positive change to an industry which is so conservative. It is almost like the "win" is there for the taking and no one has bothered to take it before Guidewire arrived on scene. Guidewire demonstrates its aptitude by winning in spite of the monster challenges it faces, both in the industry and of its own making (see below). Guidewire's company e-culture is very strong, with an advanced and mostly maintained Wiki and a plethora of quite active mailing lists. Unlike a lot of community mailing lists, there is almost zero venom or disdain for silly questions. That shows a great deal of organizational maturity and increases the odds of having everyone participate.
Cons
As mentioned in the other reviews, the NIH (Not Invented Here) Syndrome is exceedingly strong in this organization, to their extreme detriment. The NIH doesn't only have negative effects on the engineering arm, but has absolutely crushingly detrimental effects on the services arm and ultimately the end users. The travel policy for the services employees tends to be on the burlap and cardboard side of the fence. As another reviewer wrote, Guidewire is extremely frugal with their money, which is fiscally sound, but it does invite some harsh conditions when traveling or awaiting a new laptop. The opposite side of that conservative-industry coin mentioned above is that requirements are exceptionally hard to come by and failure to meet these imaginary requirements are met with above average skepticism by the end users.