Some people prefer the Palm or other series of handhelds, but a thumb keyboard and the ruggedness of the BlackBerry is an attraction. While many prefer Palm as a PDA, there are people who prefer the large comfortable thumb keyboard and prefer to use the BlackBerry as a PDA. (I'm one of those people -- I don't need all the features of DateBk5 for example, but I love the convenience of being able to rapidly enter Calendar appointments on my BlackBerry spontaneously on a spur of the moment).
An average person can eventually learn to thumbtype about twice as fast as they can Grafitti, which is another attraction. People who Grafitti at 40 words per minute, can often learn to thumb type at least 35 words per minute on the BlackBerry after a while. I am faster than most though - my test records are 40.1 WPM Grafitti/Block Recognizer in the Dom Perignon III contest by Fitaly, and 72.4 words per minute on a BlackBerry 950 keyboard and 65.0 words per minute on a BlackBerry 8700r keyboard. (Yes, these are real benchmarks. 363 keypresses in 60 seconds.)
If you need to use a BlackBerry as a PDA, check "Tips, Tricks, Keyboard Shortcuts" and "BlackBerry Calendar Tricks" of the BlackBerry FAQ
and also check out PocketDay, BBToday, and Dynoplex eWorks as various alternate PIM shells that are available.