i shelved my team six weeks ago ago cuz i was bored and just played on my mage (pally tank/mage/3 shammys), about 2 weeks ago decided to finally level up my DK and been leveling him (with help of 2 shamans) for the past 2 weeks. Just hit 80 yesterday after about 3-4 hours a day (8-10 on weekends), with 2 shamans in tow leveling was a BREEZE and super fun and easy - I quested almost all of it, and had full rest XP the entire time (would take a break every few days to raid on my mage).

My DK already has gotten 60 badges in the past 24 hours and raided naxx10/os10/both voas and is almost in full epics already (hes a BS so I did craft a ton of stuff and dropped about 10k in trade buying epics too). So I'd definitely say a 2-4 week time investment is worth it, especially since DKs are crazy fun and imo very, very good multiboxer tanks. even in 3.1, much better than warr/druid (and slightly better than pally). i've already got bronze drake on him too