Good question. It really will depend on personal preferences. I really like the RIM Playbook and was going to get a subpar BlackBerry upgrade along with the Playbook tablet. Now that I'm getting the Thunderbolt I do not need the Playbook since the Thunderbolt will fill my needs and I will still have my laptop if I need to supplement it. I will however keep my eyes on some used tablets to see if I can get a great deal on one.
I bought the xoom because I missed my broken smart phone. But the two devices are different enough that I think its worth having both. The phone I'll carry with me and have many duplicate apps, but the tab is what I'll use around the house instead of the laptop.
And right now the xoom is expensive kindle.