Hi, I don't know if this has been subsequently fixed (the original post was 2013).
Could I please +1 the original author as I have exactly the same problem. I have 500 items in my vault and at least 300 are rarely used, but might be there as storage for family password secrets on their behalf, for example.
As a result, searching can bring up 8-12 items with the same name. I would appreciate a fix which could be done in a couple of ways:
1. The format suggested where each item could have a tick box saying "don't search" (Site -> Edit -> Advanced)
2. A shortcut right click menu on one (or multiple) items that lets you do the same as above, but from the main listing screen. Much more convenient.
3. A folder (eg "archived") which is not included in the search. Even more convenient and the easiest and least coding for Lastpass to do.
4. DON'T DELETE the items in the trash! It's not like you have a storage problem. Just keep everything and then I can find the items I need in there.
I'm not really sure any more what Lastpass do with their money. I've been with them for years and in my opinion version three was fine. Version four seems like an annoying cutesy interface upgrade that has basic workflow failings. It really wouldn't take any time to add a single menu item to the right click and save us all the effort.