Most I've made in a single day would be my $800 I took from a $1/$2 NL cash game in just over two hours (I was newly 17 at the time)
Most I've ever lost in a single day was $10.
I've only done one real cash game, and that was mentioned above. I probably played like a donk compared to them, but I had great cards and some huge pots that night, never dropped under my $100 buy in, and I doubled up in one hand after about 20 minutes.
The only reason I've never lost more than ten is simply because I put myself on a $10 a week limit (because I've not actually built a bankroll yet) to keep myself in check, and 99% of the time I play it's $5 home games with a few buddies.
I`m very careful with BR management, Estelle. I feel it is a key element in success at poker. I am sure that there are many players out there who are more talented than me at the table, but who have been less successful overall because they don`t get the wider picture.
Without meaning to diss anyone, you can see it in this thread. Strong players who have taken big hits on days when the cards were against them.