How many times can you get Moxxi's Good/Bad Touch weapon?
Possible spoiler: if you tip Moxxi $15k, she'll either give you Moxxi's Good Touch or Moxxi's Bad Touch. Does anyone know how many times you can tip her to get the weapon? FYI: I tipped her $15 at level 11 and got a level 11 Bad Touch, then I tipped her again at level 15 to get another level 11 Bad Touch. Now I'm over level 18 and I have tipper her over $60k and I still haven't gotten a new weapon from her. So based on my experience (on the Xbox 360), you can only use this twice, but I have read else where that there's no limit and the weapon scales to your level (which it did not for me on my second attempt).
I think this question should just be added to this question: http://gaming.stackexchange.com/questions/84799/what-does-mad-moxxis-tip-jar-in-sanctuary-do
You can get em infinitely but the amount you have to spend is totally random. It could be 100 or 1000000 but you should leave and enter the town after you get one so you don't get the bug seen in Schottlicious' answer.
Thank you. After reading your answer, I decided to dedicate some time to verify this. I was able to get guns at varying amounts like: 48k, 181k, 57k, 172k, and 140k. (Unfortunately, they were all Good Touches.)
Also I think you need to wait for Moxxie to stop talking each time she says something for the next chance to occur.
Use only the $100 tip and spam the key/button as fast as you can. It will block you once it procs. I usually get it within $2k-$6k. Tipping $1k isn't necessary :)