This is somewhat OT, more on the lines of a tip...
But FWIW, I think I've finally started to figure out why I seem to have a problem with the APPINT OSNAP not working sometimes, particularly with drawings I get from architects (at least in 2004). I think it has something to do with the extended objects created by vertical apps such as ADT and LDD.
I think the way the bug works is that it is impossible to select one of these objects as the first item in an APPINT if the item is in an XREF. I know I have this problem a lot with stuff I get from architects, and I think I've also had the problem with things like alignments. As an example, say I have an alignment in an XREF. There's a line crossing it. I can get the intersection of the line and alignment by using APPINT if I select the line first, then the alignment. However, I can't select the alignment first; the alignment is invisible to the APPINT OSNAP. This is only a problem for the first item; I can select the alignment as the second item with no problem. Also, other OSNAPs such as NEAR and the normal intersect seem to have no problem.
This problem doesn't crop up much with Land, but it does with stuff from architects, where whole sides of buildings are some special ADT object. I've discovered I can fix the problem by going into the architect's drawing and exploding the offending items.
I may not quite have all the details of the bug right, but it was annoying the hell out of me for quite a while until I noticed this much of the pattern.