no concrete figures here, but the new Xbox's are not having the issues the older ones did. So maybe it is time. But if u don't, be sure to give Resistance2 a good hard look.
oh, and I just sent my first 360 in. One week turn around. The second one we got(when the first died) runs cooler and quieter. Have not had any issues like locking up or anything with this version. But still carries the 3 year Red Ring of Death warranty.