I mostly sell downloadable software but as of a week ago it is a web application if you squint at it.
Support is via email, and my general promise about it is "I do my level best to get back to you within 24 hours", which I achieve with approximately 98% regularity. (My price point just doesn't support phone calls. Happily I'm overseas from most of my customers, which is a great way to convince them to play ball on that issue.)
I love talking to customers but I hate doing support, because that means someone is having a less than optimal experience. Well, two someones, since writing email is no more optimal use of my time than waiting for my email is optimal use of theirs.
Accordingly, I spend a lot of time stopping support incidents before they start. This means writing and rewriting and re-re-rewriting copy in the web and application to be more comprehensible, illustrating things with pictures, and providing people with self-help options.
Example: a fairly key issue with downloadable software is getting people their registration key. It gets emailed when they purchase. But some people don't get it (spam filters, customer error, etc). So I displayed it after checkout, with instructions on what to do. But some people won't get it (failure to click through to last page, customer error, Internet failures, etc). So I provided instructions before the event (to check the spam folder) and provided a registration key lookup feature. I also made the app sniff registration keys off of the clipboard, which squashes many copy/paste issues before they start. (There are NUMEROUS ways for an unsophisticated user to fail at copy/paste.)
I keep categorized records of what causes issues and how many I get. (I worked in Customer Support a long time ago, and old habits die hard.) Relative to the number of sales, its down about 90% compared to my first year in business. I still have lots of room for improvement -- I'm thinking of a way to totally eliminate registration key entry for most users in the next version, for example. (It is fairly easy after you have web connectivity baked in.)