I learned quickly that while the iPAQ was a great PDA, I used the onboard storage up quick. An e-book or two, a map or 3, maybe a couple of mp3, all of your "pocket outlook" files, avant go content and, heaven forbid, a short video file and you don't have any memory left at all... you can't even rub two bits together!
If you don't want to spend the coin for the PC Card expansion pack and battery time isn't a big issue to you, then this is a great solution. You can throw in any of several compact flash modules or, if you are a real space junkie you can use an IBM microdrive in it. At about a fourth of the cost of a PC Card pack you can add in that extra 128 mb. A warning tho. Given the opportunity to add in more storage, you will want to. I think everyone who can will want a Microdrive in this thing at one point or another. Sure, it drains the battery a bit more but in my opinion that is more from you using the content you carry more often and not a serious drain from the expansion pack.
Happy computing.