Pros
Reasonable (but not great) benefits; large enterprise means you may be able to find work in other locations if you need to move, and they'll try to find you another job if your contract ends; stock price and management stable, if not stellar. About 90% of their work comes from government contracts, and the large majority of that from DOD. They're serious about ethics, and have several ways to report issues.
Cons
Organization is stove-piped in divisions, and competition between them means one division will torpedo another if it gets the chance. Bonuses and pay raises politically driven. Regional and project managers can run their groups like fiefdoms, meaning your employment experience highly depends on the integrity and competence of the staff at that level -- if they're good, you'll like SAIC, and if they're bad, you'll mostly be unhappy. They're stingy with educational opportunities because the costs are considered an extra expense, and managers looking to reduce their expenses will cut training budgets first (or make the application requirements impossible to comply with).