Say for example I use a particular package and want to say "Way to go maintainers" is there a way for me to do this?
I think your question is a bit open ended and probably more a discussion topic than something we can handle here on AU but I will try to answer the question in the spirit in which you asked with my personal experience.
A wise man I respect once told me "Open Source isn't a spectator sport, it's a participatory sport." Or something along those lines, I don't remember the exact lines. Like this site, it's pretty much about paying it forward.
- Help someone out here.
- or locally. Or anywhere else for that matter.
- or contribute to Ubuntu directly.
I can't speak for every Ubuntu developer, but in my experience the best way to say thanks is to help the next person; at the most fundamental level projects that depend on community participation get better with more participation from more people.
You could host an Ubuntu release party or jump on to IRC and into some of the ubuntu prefixed irc channels and thank people. Thank the devs by talking to them on twitter, etc.