I picked up an HP Touchpad a couple of days ago and thought I would jot down some impressions. I have an iPad1 for comparison and I fondled an iPad2 in passing at a local retailer so I'm not an expert by any means.
1. Hardware: TP is the same size and weight as the iPad1. iPad2 is slimmer and and lighter.
1a. TP has stereo speakers and iPad1 only a mono speaker. TP sound quite good.
2. Speed: TP falls in between the iPad1 and iPad2. It is noticeably faster than the iPad1 and all the tech reviewers say the iPad2 is a bit faster.
3. OS: webOS was made for a tablet. I don't want to take anything away from Apple and iOS, but webOS is, IMO, and improvement.
The biggest thing is multitasking. I never realized how limiting not being able to multitask was on my iPad until I got the TP in my hands but you can have many web pages and many apps open and running at one time. Nice.
I like the virtual keyboard on the TP better.
4. Browser: the stock TP browser is better than Safari. It's faster than iCab. It runs Flash pretty well. The browser is important to me since that is what I will use the TP for most.
5. Apps: 300 tablet specific apps at launch. They have most of the basics here. The Amazon Kindle app is a placeholder while they work on it - disappointing but at least it is coming. Email is good, calender is good. Skype is built in but I have not used it. You also can use about 4000 webOS phone apps. which appear small screened. For example Pandora Radio is a small screen but the interface is so simple there is no reason to make it larger - it works just fine.
TP vs. Android vs. iPad: Just based on reading I would say that TP beats Android tablets running Honeycomb right from the start. Better interface, more tablet specific apps, multitasking, speed.
iPad2 is still a front runner. However, if you are wary of getting into Apple's walled garden approach then HP starts looking like a good alternative:
1. OTA updates for TP. You don't need to connect to computer or iTunes for OS updates.
2. USB file transfer. I've not tried this yet but I'm told that the TP shows up as a drive when connected to computer via USB. You can just drag files into appropriate folders on your TP. Again no iTunes acting as gatekeeper.
3. Linux core to OS.
4. HP allows third party patches to the GUI to extend capabilities and "homebrew" apps in addition to official apps in the catalog.
Bottom line: I like the interface a lot. I love multitasking. No regrets on buying it and I think it is worth putting on your short list if you are shopping for a tablet.
Added:
Here is the most comprehensive (long) review of the TP I've read yet:
http://www.precentral.net/review-hp-touchpad