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.