No such thing as a perfect team. I wish people would get over this idea of perfection. Even the 72 Dolphins had weaknesses.
As far as the Packers go.
Their weakness is pass rush and secondary depth.
With the pass rush, they're going to rely on Clay Matthews, B.J. Raji, and Cullen Jenkins to get it done. Most importantly, they're going to rely on the scheme to generate pressure. That's been done before and it'll be done again. Whether the Packers can do that remains to be seen. I have no idea. I haven't seen enough to form an opinion on who's improved and who hasn't. I also don't know what Dom Capers has up his sleeve. We'll just have to wait and see.
For the record, every team is thin after their first few corners. GB is no exception. I like Woodson and I think Tramon Williams has made some strides this preseason. We'll see though. When Al Harris is back, I think he'll take time to get back to full strength. He may never return to that form actually. Still, there is a weakness there.
As well as the LBs, Green Bay's LBs are awful in coverage. Most LBs are but I'd argue the Pack have some of the worse covering LBs in football.
However, if you generate pressure up front, then you can disguise your weakness in the secondary or at LB much easier. Solid pressure can make a below average secondary look above average. In the case of Green Bay, I think the Packers have a solid secondary, so you can imagine what pressure would do for them.