Yeah, that limit is ridiculous. I didn't find out about the limit until after the press conference, so I probably missed out on a few hundred. Also, you get a pretty funny image when you realize that Nintendo employees had to be clearing out execs' StreetPasses all during E3 so that more passers-by could get tagged.
I've wondered about this. If you have ten passes, will your system still send your Mii out to other people?
No, it won't. Because of the nature of streetpassing, where multiple passings let you leave personal messages and rate the other person, two 3DSs must share with each other, you can't do a one-way pass.
On the inverse of what MegaByte was saying, while I knew about the 10 limit, most of the time I was too busy to check my 3DS during the actual show and conferences. End result? The only gold pants Miis I have are Peter Moore from EA and some fellow named "Karthik" from Vicarious Visions. I'm sure if I had cleared out the street pass all during the show I would have had tons more, but it didn't cross my mind at several points, especially after I had completed Find Mii and the picture collection.