There will definitely be lag using some kind of VNC setup. Anything that is critical timing wise would be a problem. If you were just mining or doing some kind of heavy crafting (GMing, etc.) or dealing with your own vendors then it might be okay. I would imagine that heavy fighting or Luna would just make you miserable.
My iPad is being used by a friend for a few days, but when I get it back I'll set it up and see what it's like to play it on the iPad through such a connection.
While I prefer iPad/Macs (I play UO on Mac OS X through CrossOver), I would recommend that if you want a small tablet, to wait and see what Dell and some of the others roll out with their Windows 7 tablets - the specs I've seen would be able to more than easily run UO, and you wouldn't have the lag associated with running it through a VNC connection. The prices will be reasonable as well - comparable to iPads.
If it's a size/portability thing, for under $500 you can get a 12-inch Asus 1215N netbook which has both a dual-core (2x cores, 4 threads) desktop Atom CPU at 1.8GHz, as well as an NVIDIA Ion 2 which has 512MB dedicated graphics memory. That thing runs UO really well. It has a 1366x768 resolution which is great for UO. It's running off of Windows 7 Home Premium.
If you want to go cheaper, for around $375, you can get the 1015PN from Asus which has a 10-inch display with a slightly slower dual-core laptop Atom CPU with the same video chipset - NVIDIA Ion 2 with 512MB of dedicated graphics memory. One drawback because of the 10-inch display is that it has a resolution of 1024x600 display. If you read through this forum, you'll find people running netbooks with 1024x600 and they don't seem to mind. It also has a more stripped down version of Windows 7
Keep in mind that the EC is the client that would benefit from that - it's hardware accelerated and more graphics memory would help - both of those netbooks above have more than enough. The lead UO designer mentioned that with the EC, the graphics chipset and memory comes into play and both of those netbooks are high spec than even normal laptops from just a few years ago. As far as the CC, both of those netbooks would handle it just fine with their dual-core CPUs.
Acer has their 1830Ts which are a little more expensive. They have 11.6-inch displays running at 1366x768. They have more powerful Intel Core i3 CPUs, but their graphics aren't as good as the two netbooks above - they are using some integrated graphics.
It's kind of crazy how far we've come with such small portables. Even if you look at those things from just a year ago, the CPUs/graphics weren't that powerful. Plenty of people played UO on those early low-powered netbooks, but with the new Intel designs, with dual-core, and especially with the NVIDIA chipsets, they are great. Those things have HDMI outputs and can pump full 1080p video out to an HDTV, so you wouldn't have a problem playing UO on an HDTV
