I use the advanced searching tool to pull a list of tasks that I can complete depending on where I am and how long I have. For example, I will tag short tasks with #under15minutes or #under5minutes and I will tag things that I can do offline with #offline. Then when I have 15 minutes of downtime away from my computer I would search "list:NextAction AND tag:under5minutes AND tag:offline".

I also use tags for my "cookbook" on RTM and want to be able to search "list:Cookbook AND tag:chicken AND tag:quickfix AND tag:summer" to pull up chicken recipes that I can cook quickly and are great for lighter summer meals.

Auto-completion for tags and list names would greatly cut down on the time spent searching and let me get right to getting things done!