I think I have never lost more than 0.2 BTC in total, even tho I don't keep track fo my loses because I don't gambel enough for it to be worth making an Excel spreadsheet over it and track all of the ins and outs of money. I just do it for fun very sporadically so it doesn't make sense to worry about it.
Although I don't gamble that frequently, I feel that making an Excel spreadsheet would be fun for me. I love dealing with spreadsheets - it's incredibly enjoyable for me to crack down and crunch some numbers, create some formulas, and do whatever it is I would want to do.
I guess I would do great in accounting, haha.
As for the topic question, I've lost about 0.4 (+- 0.5) BTC through gambling. That would be my net loss, which is unfortunate albeit I've had fun with the gambling so I don't feel that it's too big of a loss for me. Maybe it's worth the money, then. Like a hobby.