Here's a quick summary (by 210delray) of the discussion :
"I looked through past posts and came up with only six in Edmunds who reported sludge, after the dealer or other service personnel pulled the valve cover or oil pan: rrinehart, tricia barbee (V6), Boca2, isellhondas, eden1, and aquatic (a.k.a. "frank" in alt.auto.toyotacamry). Plus there were two more elsewhere: "Norm" in alt.auto and liufei's post from looksmart. Did I miss any others?
The one common thread through these (at least where enough detail is available) is that the cars all accumulated relatively few miles per year and the oil was changed about every 6000 to 8000 miles, some with Pennzoil which some of you think is bad stuff.
So it seems that following Toyota's normal-service recommendation of 7500 miles between oil changes for cars that are used in short-trip driving CAN lead to problems. Still, it's fairly well known that short-trip driving, especially in cold weather, is a severe-service condition. Toyota itself recommends 5000-mile / 4-month oil and filter changes for severe service.
However, Consumer Reports (which is far and away the best source for LONG-TERM reliability information) indicates close to stellar reliability for the Camry engines, 4-cylinder or V6.
Still, sludge would not manifest itself to the average consumer UNLESS it caused more serious problems, such as seized engines in rrinehart's and tricia barbee's cases. (It would be nice to hear from them to see how they made out.) So maybe some (many?) people have sludge but don't realize it.
Fxashun claims that the presence of sludge can be deduced from deposits on the oil cap. Others say that at least the valve cover has to be pulled first. I would tend to agree with the latter, unless maybe the cap had an half-inch-thick buildup of the stuff. Fxashun: can you tell us how many of the 50 or so caps that you checked had thick buildups? And NO other car models had buildups anything like the Camry 4-cylinder?
Then there's the possible related problem of valve stem seals going bad, as happened with my '97 Camry 4-cylinder, with only 57K miles. (Other posters in edmunds have had this probem, not necessarily with sludge). I changed the oil and filter following Toyota's severe-service schedule. Why did the dealer say, when I described the symptom of blue smoke on start-up, that the first thing they were going to do was check for sludge? Does Toyota know something? (Luckily my engine was said to be "fairly clean" [whew!] and the valve stem seals were replaced under the powertrain warranty.)
Let's try to keep this going without this getting into another shouting match between the two sides. Personally, I still love my Camry, but if there's something going on, let's try to get to the bottom of it."