I would do the deal if I could turn around and trade Dalembert for something useful, or find a third team to take him.
You don't think Dalembert would be useful? Great rebounder, shotblocker and finishes everything around the rim with dunks. I'd prefer him to Sheed at this point and I'd rate him about equal to Perk (better rebounder/athlete, inferior post defender).
Problem is he has a 7.5% trade kicker which would make him even more overpaid in a trade.
Dalembert is equal to Perk, and is better than Sheed... 
I sense skepticism. Let's compare:
Samuel Dalembert:6'11'' 250 lbs Age: 28
PPG: 7.5 (09-10)
8 (Career)RPG: 9.8 (09-10) 8.3 (Career)BPG: 2.2 (09-10) 2 (Career)SPG: .6 (09-10) .5 (Career)FG%: .519 (09-10) .523 (Career)
FT%: .838 (09-10) .697 (Career)MPG: 26.1 (09-10) 26.4 (Career)
Kendrick Perkins:6'10''
270 lbs Age: 25PPG:
11.6 (09-10) 6.3 (Career)
RPG: 8.2 (09-10) 6 (Career)
BPG: 2 (09-10) 1.5 (Career)
SPG: .3 (09-10) .3 (Career)
FG%: .620 (09-10) .564 (Career)FT%: .588 (09-10) .608 (Career)
MPG: 28.8 (09-10) 21.9 (Career)
Okay, I've bolded the areas where one is better than the other. The stats aren't particularly surprising. Sammy D and Perk are fairly similar players.
Physically, there's only an inch difference between them, and I think in terms of how they play it's negligible. Perk is a bit heavier than Dalembert (mainly muscle), which is fairly significant. Dalembert, however, is definitely a better rebounder. Perk is a better offensive player, scoring more points (mainly in the last couple of seasons) and posting a higher FG % (though I think Sammy D has a bit more range). Dalembert is a better blocker, though it's pretty close. He's also a better free throw shooter, and plays fewer minutes per game to put up his numbers.
I won't bother comparing either of them to Sheed because, frankly, they're both very different from Sheed and a lot younger. I think it's safe to say they're both more valuable than Sheed at this point.
In any case, other than intangibles on defense that don't show up in stats (like Perk being able to bother Dwight Howard more on the block), I'd say Perk and Dalembert are pretty even. Dalembert is actually significantly better in a few categories.
Overall, I think he's definitely a downgrade (especially since his contract is a lot bigger and he's a few years older), but I think if we're getting Iguodala in return for Ray in a trade, the excess of talent coming our way in that swap more than makes up for it.