I pumped for both my kids from 3mo-1yr during the day when I worked. With dd, I used the regular PIS and with ds I used the PISa..I definitely pumped more w/ the PISa. I don't know if it was because my body was used to the nursing/pumping thing by then or it was the pump...but it was more. Since I'm not a prolific pumper (nursing was just fine..it was the pumping I had difficulty with) it was definitely worth it for me to go with the PISa.
As for storing....
I pumped into the medela bottles that came w/ the pump. I had some extra bottles the second time around!
The freshly pumped milk was stored in the cold pack section of the pump w/ a freezer pack and when I got home I would even out all the bottles to single servings. I would never pump right into bags because they aren't as accurate when measuring out the milk (I tested it w/ the bottles and they were always WAY off).
Once the milk was in the single servings I poured each one into a separate milk storage bag. With dd I used the Gerber bags and with ds I used the Lansinoh. I prefer the Lansinoh now, but when I was pumping for dd they didn't have zip lock tops. The Gerber bags are not bad by any means and they are a bit less expensive than the Lansinoh. The cheapest place I've found the bags was at Target when they had their "baby feeding" sales. I would stock up and purchase 10-20 boxes of bags at a time!
Typically I would place all the "fresh" milk I pumped that day in the fridge for dd or ds to use the next day at daycare...except for one bottle's worth. That would go in the freezer ... flat (Don't stand it up, it freezes into a big lump of milk that is difficult to store and defrost. Plus, it makes all these hard corners that make it more likely to get a hole in it and leak!...I know this all from experience!). After it was frozen it was stored on it's side in date order and each day dd/ds would get one "frozen" bottle and the rest fresh at day care the next day. On Fridays I would freeze all of my pumped milk and on Mondays dd/ds would drink all frozen milk (minus any fresh I managed to pump on Sunday).
We also left one frozen bottle in the freezer at day care in case of emergency (leaked/spilled milk or if dd/ds was super hungry!).
I really became a pro at this. There are a number of great resources for pumping moms out there. A VERY active and helpful bunch is at Yahoo Groups and iVillage has a pumping group as well. You also may find some info at pumpingmoms, promom and kellymom. All three are "org" sites.
HTH!