Would the use of nested tags help with what you want to do? Say you need to see all notes with both #tag1 and #tag2, you could use the #tag1/tag2 nested tag expression. One limitation currently is that you can only use two tags in combination at one time. My understanding is that the developers are working on deeper tag nesting so that you could then group three or more tag combinations. Hope this helps.
It seems there is a clean, simple solution. You can put multiple tags in the search box. Just saw this in another thread. So you can put #tag1 #tag2 #tag3, etc. and find only the notes that contain all the multiple tags.
Multitag search it is very important feature for me. Unfortunately without it – the app is useless and doesn't suit for many notes. I really want to see implimentation of this like in Raindrop.io app for bookmarks.
To add to what John said about searching/filtering by tag (#2), it would be nice to be able to use wildcards to search/filter by tag. For example say I have the following tag structure (shown at the bottom) and I want to filter out everything but the lectures ~ it'd be awesome if I could run a filter/search using wildcards such as #*lecture* to get all lectures from all classes. Or I could filter/search #*calculus*lecture* to get only the calculus lectures (excluding anything from physics and also excluding any calculus discussions and labs).