"AdAway, Titanium Backup, Angry Birds space".
Check. Ad removal is non-existent. Being a wp7 user it also struck me as odd but backups... non-existent. Angry Birds Space; yups... As in nope, but "yups; you're right there".
"HD Widgets or BeWeather"
This particular app. isn't available to my knowledge, but in all fairness there are plenty of very good alternatives. My personal favourite being WeatherMaster (which GPS location weather works quite well IMO).
"a good dropbox or box client that can sync my photos automatically (skydrive doesn't cut it, too cumbersome to work with linux)"
Cumbersome? You do realize that you can access SkyDrive from within Linux using any decent WebDAV client? You should easily be able to access this using KDE or Gnome filemanagers.
"Google plus, fring or nimbuzz"
Both aren't supported, correct. However, when it comes to IM and such there is the alternative to utilize Live's messenger or Facebooks chat features. Not the same, you're right there, but I figured I'd mention it nonetheless.
There is Skype but... With the limitation that it cannot receive incoming calls as if they were normal calls (app doesn't continue to run in the background).
"Decent gmail client"
GMail / Google Mail is natively supported by the OS.
However; not being familiar with gmail myself keep in mind that I have no idea if you refer to specific features which could very well be supported in a native gmail client and not in the default WP7 mailclients. In all honesty; wp7 mail clients have some pro's (IMO) but also con's (for example; you can't easily use your gmail account and tell it to use "mydomain.com" as sender because it will force you to use your gmail alias; even though "mydomain.com" can also be mapped to gmail).
Thanks for your comment!