Many people tell me that 1 warmth is enough, but just one skill point wont do crap.
True, level 1 warmth isn't too significant. But most people are assuming you have some +all skills equipment, and after say... +6 skills it goes from 30% regen to 102% regen, which is a noticable difference.
1 point is enough if you have decent EQ. But if you're untwinked, just starting out, or are just plain poor, then a couple more points will definitely come in handy.
on all the sorcs I have built I put around 5-7 warmth. thats without using Esheild so only casting or teleing takes my mana down. with Esheild you may want more. I have +3 fire skills using a +1sorc skils dual res ammy, +1all tarnhelm, +1 fireskills magefists, and I am puting around 3-4 skill points inwarmth. I am a Orb/CL sorc, and I need a bit more mana regen.
also the mana regen on magefist and manald heal rings adds to youre total mana regen, so you can get more regen that way.