After playing with the HDMI dock over the weekend, I thought I would write up a short review to answer some of the questions I had trouble finding answers to before buying it. Feel free to post any other questions and I'll try to answer them.
Wireless USB mice and keyboards work, and not just in Webtop mode but in Mirroring mode as well! It was unclear to me if they would work at all, since only Bluetooth keyboards are specifically mentioned as working wirelessly, but I grabbed a Logitech keyboard/mouse combo on sale for $29 and it works out of the box without having to install any software. Just plug the USB dongle into the dock and go. It's great having the mouse in Mirroring mode to browse through the Netflix app, having the keyboard to type emails and Google Docs, etc.
Netflix is just about perfect in Mirroring mode now that the audio clicking bug has been fixed. I watched the entire first season of Mad Men without a single crash or problem of any kind.
Firefox addons work in Webtop mode. Mouse gestures and adblock are especially useful. You can also synch bookmarks if you have a Firefox account (I use Chrome on my PC so I haven't tried this yet). Firefox imports your bookmarks from the default Android browser when you first open it.
The Hulu website works in Webtop mode! And Firefox adblock prevents the ads from playing (you still have to sit and wait while they count down, but you can open another tab while waiting).
YouTube, Vimeo, etc. look fantastic streaming in 720p on a big screen.
Alt-tab works in Webtop mode to cycle through running apps, just like in Windows.
The phone fits in the dock with or without a case, thanks to the removable insert (same as the normal dock).
You can scroll web pages using the remote. This is a small thing, but it's fun to lay on the couch surfing with the little remote instead of having to use the mouse or keyboard.
The biggest problem with Webtop mode is the memory management. Even with only one tab open in Firefox, I'm always having to kill processes in the Android task manager to get the "Low Memory" window to go away. This is especially annoying when you're trying to watch a video, because there's no way to hide or dismiss the window. It also seems to be too conservative about triggering the "Low Memory" warning -- even with 10% or more free RAM free it sometimes pops up. I would rather it wait until 5% free or less, or better yet, let the user configure the threshold.
Not the fault of the dock itself, but I was disappointed to find that the HBO GO app blocks HDMI out from working. Not sure I understand the logic here since you have to be an HBO subscriber to use HBO GO in the first place -- so why would they care if I watch it on the phone or on my TV? The HBO GO website does work via Webtop in theory, but it's an unwatchable slideshow in practice.
The remote doesn't work with Netflix, YouTube, etc. This was a disappointment because I had hoped to be able to advance, rewind, etc. with the remote. The play/pause button doesn't even work -- it opens the Music app instead. The only remote buttons that work in Netflix are the volume controls and mute.
In Webtop there's no way to delete the shortcuts that come pre-installed on the desktop. So for example, I use Google Music Beta exclusively, but I can't replace the old Google Music shortcut on the desktop. There's also a useless "Webtop Apps" shortcut that just takes you to a web page with a list of Flash sites, which the Help files claim you can delete, but I have yet to find a way to actually delete it. This is a pain, especially since there's limited space for shortcuts.
Custom shortcuts can only point to a website -- there's no way to create a custom shortcut to an Android app (such as Google Music Beta, see above). Also (more an annoyance than a problem) custom shortcuts don't display the full-size icon of the webpage, but instead display a shrunken postage-stamp-size version of the icon surrounded by a white box.
Occasionally the Webtop option doesn't appear when docking the phone, or it goes straight into Mirroring mode even though I haven't checked the box to always use that option. Not sure what's causing this one, but reseating the phone in the dock usually fixes it.
Overall I think the HDMI dock is a bit overpriced at $99, but if you watch a lot of Netflix streaming, want to watch Hulu or Vimeo on your TV, or like the idea of surfing the web on your couch, it's a fun device to have. Hopefully a future update (or maybe a custom ROM?) will fix the memory management issues and other small annoyances. I'm also hoping someone will write an app that makes the remote work with Netflix.