It might be a better idea to post below as a feature request to Gmail team directly, but I post it here because of two reasons:
1) I'm rather busy at work to find their blog
2) let's check Google's track_everything_happening_on_the_web property
About spam again. Recently I have been receiving quite a bulk of these pleasant messages (giving the unique opportunity to enlarge something on a recipient's body etc) - which results in about 100+ messages / day filtered out to the spam folder.
Not sure about the majority of e-mail user habits, but I have an attitude to check all the spam messages (don't worry, only the titles; well the body rarely as well) and get rid of them manually, rather than leaving the engine to automatically delete them after N days. I should notice the precision of the spam filtering algorithm Google has in Gmail: it works perfect in my case. But still even the tiniest 0,(0*)1% probability to overlook the valid message in spam folder may give hard times and irreversible processes in my brain, which I do not want to happen.
So my idea follows next. Suppose I have 10 pages of junk piled up in the spam folder. When I open one page and start looking through the e-mail topics, I obviously spend some time (like 2-3 minutes for 100 messages). Once I have done this, I may or may not proceed to the next spam page, but with no regard to it Gmail marks internally the page as "read". When I sign out or after a while (another configurable parameter), Gmail silently deletes all the "read" messages.
For the sake of flexibility there can be the third feature: a button (or a fixed option) , explicitly prohibiting to silently remove messages even though they have been read.