Are Tablet PC’s good for using Photoshop?

I was thinking about buying a new computer and I figured that I could get a Tablet PC, preferably a slate.

The main functions that it would have to serve would be Photoshop to draw and stuff and connect to the Internet.

Would a Tablet PC be a good tool to use in order to draw in Photoshop or should I not even bother.

I also want a slate Tablet PC instead of something to connect to my computer like a Wacom Tablet (which I already have) because I don't always feel like sitting at my desk to draw and I want to have something that is portable.

I know that Wacom has a 12" Touch Screen Tablet that connect to ones computer and I could draw on that, but again, I don't always feel like sitting at my desk and drawing.

Any suggestions will be greatly appreciated.

Thanks.
What is a good Tablet PC, preferably a Slate without a keyboard, for using Photoshop?
I guess what I would need would be something that has a good touch screen. Something that does not lag when I start drawing. Pressure sensitivity with the pen would be good.