This is something that I wanted for a long time, really wish to see this in the upcoming release of ASP.NET.
In a few words, I cache items in the ASP.NET cache with sliding expiration, in some cases I need to peek an item (i.e. get its value) without affecting the sliding expiration time. I really need this.
I asked a question about this long time ago:
http://forums.asp.net/p/1277310/2432439.aspx