Yeah – I also have that problem. I’m using astercity.net as my ISP and with proxy I can’t submit to some LL (link-o-rama for example) who use scripts detecting IP – in this case I get an error saying: "you can’t submit – you’ve already submitted during last 24 hours" – of course I get this error only if some webmaster using astercity.net submitted before me
Fortunately I’ve got also access to different ISP with different IP, so it’s not a big problem for me, but for webmasters who don’t... well – first wake up, first submit