I understand your question. There are a very few that I will enter via the e-mails that the sponsors send. I find that it is almost always better to come back here to enter, though, so the red blocks turn green and I have an easily accessible record of what date and time I entered various sweeps. As you say, it is especially easy to enter the 24-hour sweeps from the Lucky List because the time is tracked for you.
The CompUSA and Tiger ones I sometimes enter from my e-mail because there is that second e-mail that they send to complete the entry.
The $12,500 ones I personally only entered once because after paying the taxes on $25,000, there won't be that much left of the $12,500. You have to pay the taxes on the $12,500 that goes to the charity as well as the $12,500 that goes to you. Granted, you still come out ahead financially. Anyway, because I don't enter those, I have no idea if there is anything special about them that makes them easier to enter from e-mail.
I almost always check the blocks NOT to receive mail from the sponsors when they provide that option.
Best 10/2009 win: 47inch LCD 1080p HDTV including a TV stand, Nintendo Wii and two games (1 of 10 Grand Prizes)
Best 11/2009 win: Kindle (1 of 7 Grand Prizes)
Best 12/2009 win: $5 Home Depot gift card (1 of 10,500 fourth prizes)
Best 1/2010 wins: Loacker bag with 8 mugs (1 of 1000)--from my very first sweeping entry in the New Year!
................................. Philips Prestigo Universal Remote Control (1 of 5 remotes out of 50 second place prizes)
................................. $5 check from Cheerios (now a total of 4 out of 40,608) actual money--woo!
Best 2/2010 win: stainless steel tongs, $2.66