To add my 5 cent worth:
Email appears on the Blackberry and in Outlook. Deleting it from the Blackberry doesn't delete it from Outlook. Deleting it from Outlook deletes it from the Blackberry after a few minutes.
You can change this setting. When I delete mail in my Blackberry, I have configured it to ask me whether to delete on Handheld Only or on Handheld & Outlook.
You can also choose Reconcile Now if you want emails deleted in Outlook to immediately disappear on the Blackberry.
Only the inbox appears on the Blackberry - no sub-folders. (However I reckon you could set it up any way you wanted)
This is usually the case with synchronised mail on PDAs etc.
After all, you don't want to fill up the memory too quickly.
Attachments can be opened but I don't find it useful (for excel spreadsheets).
The Word viewer can be handy although tables are a pain to navigate, same for the spreadsheet viewer. Both can be useful but I find it is better to ask people to send short docs in the body of the email instead rather than as an attachment. Also will be cheaper due to less GPRS traffic.
You might also consider a smartphone (like the Sony-Ericsson P900 series). Only one gadget instead of two to carry around. But it's bigger than it looks on the web. Also, a friend of mine has a P900 but he doesn't like it because you can't get a car kit and it's always ringing 999 when it's in his pocket. I don't know if his comments are true.
I switched from the P900 to the combination of a Blackberry and a small(er) phone - the V800.
I find that the smaller phone is much handier when out and about, in the pub, etc.
I now only carry the Blackberry when I want to be contactable via email, and I have no qualms about turning it off on holidays, contrary to some of the views expressed in this thread. Mind you, I do find it is useful to switch it on, say, the day before I go back to work from a holiday, so that I can delete spam and perhaps identify any important emails to give my attention to when I get back to work.
Plus, I find the remote synch of outlook calendar entries very useful - you don't have to wait till you dock the device and synchronise, as you do with the S-E P900 and similar Palm or Symbian devices.
BTW, the S-E P910i has the Blackberry push client, so mail
will come to you rather than you checking for new email manually, but I still prefer to carry two devices.
When someone rings me and asks me to check my diary for an appointment, I can talk on one phone and look up stuff on the Blackberry. (Admittedly, you can also do this on a S-E if you use a handsfree headset, but it is still a bit awkward to do when on the go.)