SUS is free and works pretty good, but as Saltin said, it's only Hotfixes, no service packs. SMS is better, but not free (not by a long shot), and will do many more things (including service packs). I'm actually in charge of implementing something exactly like this for my company, and right now I'm experimenting with SUS and finding it rather limited. It's probably what we will go with due to budget constraints (apparently it's cheaper to pay IT staff to go around and do it by hand, not sure how they figured that one out). In any case, SUS is still a pretty good way to keep control over the systems, but it's not so great as far as abilities and flexability goes. Use it if solutions like SMS are out of budget.