I exclusively pump, have done so since day 3 when my milk came in, and my experience is very different to those above. I've been doing it now for 13 weeks.
I pump three times a day on both sides until my breasts feel completely soft and empty. This will usually harvest enough milk for more than a days worth of feeds. It takes me a couple of hours in a morning and then an hour-ish around 3pm and then another hour-ish at about 8pm. The whole lot goes into the fridge or the freezer for use during the day or more long term storage.
I've very rarely pumped overnight, maybe once or twice if I've felt a bit uncomfortable.
I do not find it hard work at all. If anything, it's more convenient than breastfeeding because feeds can be done by someone else and are done at bottle feeding speeds. As it is breastmilk, feeds do not increase in volume as the baby gets older either. The tend to take an average of 750 ml every day throughout the first 6 months.
I, along with other exclusive pumpers, have found you really don't need to pump every two hours (aping a newborn feeding schedule) so long as when you pump, you pump to "emptiness" and you pump before your breasts get too engorged.
I suspect pumping when your newborn has a feed (ie. pumping every two hours) is why some mothers end up with three months of breast milk in the freezer; they are essentially over-pumping.
I've also found that pumps with hard plastic cup flanges are poorer at drawing milk than those with a silicon inlay (I got significantly less pumped milk using a medela than my cheapy tommee tippee pump).
I really don't know why there is such a strong negative reaction to exclusive pumping. I suspect it is because people believe they need to pump very regularly so it becomes very time consuming. I was told by a breastfeeding specialist that there was no way I'd keep it up in even the short term. Yet here I am, three months on.
I find it massively convenient because dd is entirely breastmilk-fed, anyone can feed her, and we can go anywhere in between pumps without me having to think about where I could breastfed if she got hungry. I just take a couple of bottles with me. It also means that I can go out in the evening (sometimes I will pump earlier and later so that I've 7pm to midnight free).
All that said, I do have large boobs and did start pumping when my milk came in (I started pumping because my latch went awry when I brought dd home and I was terrified of a poor latch affecting my supply in those early days. My boobs were also rock hard and I needed to drain some milk asap. Once I did, I never looked back).