Here's a quick review:
Running AppleTV 2g 4.1 (iOS 4.2.1) tethered jailbreak with nitoTV bundle and aTV Flash (black) Beta 2.
Initial thoughts are that it is hideous to jailbreak, but the aTV Flash install is very straightforward.
1. nitoTV - 7/10
Very limited functionality.
Weather plugin has limited features but works fine. The only gripe is that it is not possible to remove the default locations or any new added locations from the screens - no remove feature. Instead, you have to edit files on the AppleTV via SSH and the plugin crashes when you remove items from the plist file, requiring the jailbreak to be re-activated. Also, adding a new location requires you to find the Weather.com ID for your location. Not very friendly. However, it is possible to install the Main Menu Weather extension from nitoTV, which also requires a different cryptic location code, but is more informative.
RSS plugin is diabolical. Once again, removing RSS feeds has to be done via SSH and crashes the plugin. The display of RSS news items is fine on the main list page, but digging into the articles results in a nasty text-only page. Would be much nicer to see a decent HTML rendering of each feed.
Install Software feature enables new plugins and processes to be installed via a fairly nice menu and search facility. It covers a range of debian packages, awkwardTV (nitoTV etc.) and Cydia repositories. Featured plugins do not all work on Beta 2 and some (e.g. Groovy) crash the AppleTV. Would be better if nitoTV updated their compatibility filter for aTV Flash (black) Beta 2. I successfully installed netatalk so that my Mac could see the appleTV filesystem in Finder. MainMenuWeather went in fine. Plex definitely does not work with Beta 2 - avoid at all costs as it will get you into a restart loop. I tried manual install methods and nitoTV install of Plex and wasted many hours. It just doesn't work with Beta 2. Generally, a lot of the nitoTV apps found via the search do not work and may damage your installation. However, Install Software is a great feature to have available and will no doubt improve when aTV Flash (black) hits gold release.
2. Browser 5/10
Not the world's greatest browser, probably one of the worst. It reminded me of the pain of using the old PSP browser.
Finally, navigating between pages is a nightmare, because you have to use a menu to decide to go back a page or to enter a new URL. Would have been much better to detect other less-used Apple Remote events.
3. Last.fm - 7/10
Does what it says on the tin. A very simple implementation, but functional. I personally don't like Last.fm and would have preferred Groovy to be working or to see a port of Spotify/Pandora, etc.
Overall Conclusion: A move in the right direction, but Beta 2 is seriously hobbled by a lack of support by 3rd party developers and apps like Plex that used to work on Beta 1. Roll on Beta 3 and hopefully other codecs, NAS and network streaming, fixed Plex/Groovy and all the other goodies that should be possible.