[mgmueller]

Display Quality:
I've read some devastating reviews about Galaxy Tab. I can't confirm these reviews at all. I find the colors equally vibrant and the glare about the same.
BUT: I find the surface of both displays slightly different. I've read somewhere, Apple is using a special varnish, to reduce fingerprints. Well, I can't confirm re. fingerprints. It's the same on both. But I've got the feeling, the iPad surface is somewhat "smoother". Sometimes, when scrolling/flicking through webpages for example, I kind of "stick" to the display of Galaxy Tab. It's no biggy, but iPad seems slightly more responsive and smoother.

Portability:
I wouldn't use this as a criteria. Some prefer mobility, others prefer screen estate. Personally, I take Galaxy Tab permanently with me. It perfectly fits in my coat pocket (I've used the Sony 600 pouch, since Monday I'm using a TuffLuv 6.2" neopren sleeve). iPad to me is way too bulky. I take it on trips in my laptop bag, but I wouldn't call it a "mobile" unit.

Battery:
Coming from high-end notebooks (usually about 5 hours of battery life), I'm more than fine with both. iPad for me does about 8 to 10 hours, Galaxy Tab maybe 7 hours.
Some recommend, turning WiFi and other battery hogs off. That's no option for me, I'm using tablets mainly because of those features.

Buttons:
I absolutely hate the physical home button on iPad/iPhone.
It's helpful, having a physical button. But I simply don't like the mechanics. And I'm sceptical about its durability, when using it heavily for multi-tasking.
I very much prefer the capacitive buttons on Android units. And I prefer, having more than 1 button. On Samsung Galaxy Tab, there even is a context sensitive "search" button. Depending on the app you're in, it either starts Google or the search window of the respective app.
I love the menu button. Entering any app's menu with the very same button, whereas on iPad I'm sometimes searching for the menu.
But: Having no physical buttons on Android isn't perfect either. When any application is hanging, the capacitive buttons sometimes are blocked for a few seconds. On iPad, the physical button is working all the time, whatever might be blocking the OS.

Multi-Tasking:
A huge plus for Android.
On iPad (or did I miss something?), you can't choose. Per se, each application goes into the background and is multi-tasking.
On Android, I decide which button to press: Close the app or multi-task.
On iPad I have to double-click the physical home button, to see all the active apps. On Galaxy Tab, I just open the app "Task Manager" and see all the open apps and processes.

Boot-Time/Startup-Time
Both take about the same time to start.
But: Galaxy Tab is doing a media scan every time it's turned on. Probably due to the SD card. I hate that. It should know, whether I've taken out the card and manually did copy some media files or not. On the other hand, you can't use any SD card on iPad, so it's somewhat unfair to nag.

Expansion:
Galaxy Tab is using standard Micro-SDs. You easily can reach/change them, you don't have to fumble with the battery or something like that.
You can expand iPad with a harddisk via the official camera kit. But who would want to add an external harddisk to a tablet? So, basically iPad can't be expanded.

UI:
Very often I read, Android 2.2 wouldn't be ready for tablets yet. I don't agree. I find the UI and OS quite similar to iPad. There even are some advantages, like alternative keyboards.
Over all, both UIs/OS have their advantages and disadvantages.
iPad seems more stylish, easier to use and more polished. Android on the other hand is more open, allows for more tweaks and allows for more manipulations by the user.