Now the ISP I use is one of the biggest European-wide ISP's, and I am pretty certain that for me it would be very difficult bureaucratically to get them to do anything like configure an rDNS or raise or lowerTTL's and so on. So, I haven't tried.
You might be surprised... I have a home DSL connection from AT&T who is currently the largest phone and DSL provider in the US. A few months ago I considered moving my mail server home and inquired about a "static" IP address. It took a little digging as their first level tech support had no idea what an rDNS entry meant but I was eventually given the number for a department that did just that. They said it would be no problem and I didn't even need "business class" - just a static IP.
I also setup an rDNS for my church's email server on RoadRunner's cable network. They are the second largest cable ISP in the US and also had no problem with my request. If you have a "business-ADSL" service, I think you're entitled to proper setup by your ISP.
When I was a student, I ran my mail server off of an ADSL for 4 years, properly setup, and never a glitch. Email is resilient and will handle timeouts well. I can't see how people can complain about that when they use greylisting to force retries. Granted, in the end I opted to keep mine on the T1 at my colo. ;-)
-eric