Percy continued to get very little limelight with Order of the Phoenix, but he received enough to stir quite a controversy. Spurning one's family for one's dream is the stuff that controversies are made of.
Lets do a little Percy analysis here and flash back about ten years. This was the Percy before the prefect and head boy badges. We see a young kid a few years away from Hogwarts. This young wizard had two older brothers that experienced great success at Hogwarts while being in Gryffindor house.
Viewers who have older siblings can relate with me on this point. Percy was awed by the stories that his brothers talked about while spending their summers at the Burrow. He clearly heard about Bill becoming head boy and Charlie excelling in Quidditch. He had to be in Gryffindor.
Now lets flash forward two years. Percy is now at the hallowed grounds of Hogwarts. I can almost visualise him with bug eyes oggling at the aura that the Great Hall was giving off. He then queues up and yearns for Professor McGonagall to call his name out. After a long wait, he approaches the Sorting Hat, eagerly places it on his head, and waits.
Here, I can almost see a replay of Harry's situation. Percy knew that his two older brothers, as well as both his parents, were Gryffindors and he simply had to be placed there.
"Not Slytherin, eh? Well, if you're sure...better be GRYFFINDOR!"
Ok, now I'm not hinting that Percy Weasly will go off and save all of wizardkind from the evil Dark Lord. However, from his characteristics from the first five books, it is almost a no-brainer that he belongs to Slytherin. His unquenchable thirst for the post of Minister of Magic is unparalleled. He clearly showed in the fifth book by allowing nothing, not even his family, get in the way of his path to his ultimate goal: Fame and Prestiege.
Yes, I know he was a complete git in the book. Let's think about this for a second, though, and put yourselves in Percy's shoes. If you're yearning for a promotion, would you dare call your boss a liar and not support his decisions? Of course the situation here is a bit different, but it's all the same for Percy. All he sees is a direct path to his goal.
This path did, however, led him astray from the side of good. While he didn't exactly enlist onto Lord Voldermort's army, he wasn't exactly supportive of the cause against them. This can be attributed to what Percy wants to believe is the truth, a wrong truth that his boss and idol Cornelius Fudge was preaching. He knew he had to go along with his plans to get where he wanted.
Lets switch gears for a moment and analyse Percy's letter to Ron. While we were too busy agreeing with Ron that Percy is the world's biggest git, some fail to realise one thing: that Percy obviously didn't completely shun his family. He was completely thrilled at his youngest brother's achievement and even was worried for his safety. Yeah, I know he advised Ron to stay away from Harry, but this stems from the story that Fudge fed the ministry. This clearly was a morsel that Percy was far too eager to devour.
So in conclusion, I leave you with a few words that I think best describes Percy: dedicated, strong-willed, naive, and smart. He knows what he's doing. It's all a clever plan for him to rise to his ultimate goal. Woe to those who gets in his way.