Right now I have a lot of backorders pending, and I am curious if the current owners of those domains can see that I have that backorder on their name. Causing them to be more likely to renew...
I don't see how they would know this, unless there's a domain monitoring service that can provide you with this information. But if you've backordered several places (Namejet, Snapnames, Pool), I don't see how someone could keep track of all that.
I don't think there's a way to check that, unless someone else on the boards knows of some special trick.
There's no telling what the owners are thinking - they could be domainers who let these names drop ("expire") on purpose, or they could be business owners who were overwhelmed with other things and let it expire accidentally. Chances are they don't know the domain is going to auction or up for grabs
I think the advice about waiting until the last minute to backorder is mostly for Namejet, since once a name has entered Pre-Release or Pending Delete they actively display how many people have backordered it. In that case, it's in your best interest to wait until the last second, to not draw attention to the name.
You can place backorders elsewhere without people knowing this info.
Repeated WhoIS searches on a name might clue someone in that there's interest (if they're monitoring that sort of thing), but chances are people who let a domain expire don't have that on their radar.