I'm on Charter in Minnesota. They installed one M-card in my HD TiVo. If you go with the HD TiVo, you can get rid of Charter's HD receiver. You may want to question Charter about how the new billing will work. When I got the HD TiVo, I sent the cable box back with the installer only to see my bill skyrocket. Charter said it was because they only way they could do packages was with a cable box installed - so I had to go pick one up again. They've changed their program since then and now a cable box is not required in my area. Go for the TiVo - you don't need any other dvr service from Charter.
TiVo user since May 2002
I am currently running 1 Premier Elite XL4 and 2 TiVo HD's - all w/Lifetime