They released it end of April, I believe but had limited stock and still do. If you monitor nowinstock.net, you can get one. That is how I got mine.
I had an iPad but sold it. The experience I had on the iPad was less buggy than ASUS. Apps were plentiful within the first 4 months but finding apps on Android Market that iPad has is a challenge. You will find the majority of them but maybe different developers. Netflix, GoodReader, Toodledo come to mind. But I quickly got bored of it since I had an iPhone. Other than the bigger screen, I didn't see much of a difference.
I got the ASUS Transformer and couldn't be happier. It solved most of my major annoyances with iPad. The browser (when it works) has a familiar experience to the desktop Chrome, although a bit slower but felt snappier when compared to iPad 1 on 4.2. I can have different browsers (Full Firefox, Full Opera) and set them as default. Like when I get a link, it can open directly in Opera if I wanted to than going to Browser only. If you recall with iPad, it automatically points to Safari then I would have to copy paste or use a bookmarklet to open it in a different container like Atomic Browser to just get tabbed browsing. I can change the keyboard to include a number row! I have a file manager that can be shared by all apps. No need for each app to have its own local copy. I can many widgets such as quickly glance at the weather without having to open the app. And the best thing about all of this, I can browse the Android Market from another computer and click install to apps I like, and then they will install when you pick up your tablet. No need to be stuck to iTunes is a plus. That is on the software side.
Hardware: ASUS has an IPS display, a mini HDMI, microSD, proprietary cable to charge, and an accessory to dock to a keyboard. Hardware built is okay but I didn't mind it (minor light leak). Xoom has similar hardware specs but at $599 for 32GB and a non-working microSD currently. They don't have a 16GB. So, direct comparison is 32GB ASUS of $499 vs Xoom for $599. Samsung is $499 for the 10.1" and doesn't offer much anything else. It is an iPad 2 with Honeycomb. Processor and RAM are the same on all three. Cameras differ a bit but I would say they are all good enough for a tablet, even the iPad 2.
TL;DR: iPad is an iPhone, and ASUS is better than Xoom because of price!