I have 2 tivo HDs on Cablevision NJ as well as an HD HomeRun Prime, all with cablecards.
If you buy a tivo HD / premier, you can just go to a walkin center and ask for a cablecard, they are $2/month to rent in my area.
I have rarely had issues due to the cablecards.
Most recently I had to replace my hard drive and had to call back in to re-pair the card to the Tivo. Other than that, I can't even remember the last time I had a cablecard issue.
Cablevison is in the middle of phasing out their remaining analog channels so even if you only used analog today, you'll only get some unencrypted programming after the remaining analogs are shut off. Plus w/o a cablecard, unencrypted QAM channels don't get guide data.