Should I purchase a computer or a tablet?

I'm one of those people that wears out something or completely uses it up before I think about purchasing more or a new one.  My seven year old laptop appears to be invoking its "do not resuscitate" order and I'm in the market for something new.  I really want to have something that can be a portable credit card machine and online art jewelry portfolio viewer at art shows and events.  I've been looking at an iPad, the soon to be released Blackberry counterpart, the Playbook, and the Dell Duo, a touchscreen tablet and netbook in one.

Help!

They all look to be about the same price, so that's not an issue, but I just don't know what is going to work best for my situation.  Here's a few questions I need answered:

1. If I get a tablet, am I going to miss having a functional keypad?  For tablet users, do you have a keyboard?  Do you use it?
2. Can you do everything you want to on a tablet?  If not, what do you wish you could do?
3. Anything I should know about connectivity issues?
4. Do you have a Dell Duo and love it (or hate it)?
5. What else am I missing???

I'm not in a hurry to buy one, but could do so anytime.  (By the way, if you're reading this and know of a nerdy friend that could answer these questions, I would be grateful if you could forward this post to them.)

Opinions please!!!