Could you give me a specific example where you need to attach different documents to e-mails? I can't think of very many situations where there isn't another way to communicate the same info in a way which is bettet for both sender and receiver. Importing a filesystem and the attendant side-effects strikes me as an inelegant solution.
I work in academia. I e-mail all kinds of files to colleagues. Papers, PDFs, data sets, powerpoints etc.
If it's someone I work with regularly, I can just set up a sharing folder on Dropbox depending on how comfortable I am using the cloud for whatever I'm sending (I trust e-mail security more). But many times I'm just e-mailing publications to a bunch of people in my field to promote my work etc.
Just playing devil's advocate as I don't really care that much about that on the iPad as I think the mail app stinks in general and mostly don't use it anyway.
But there are needs to just attach files to e-mails to send to multiple people at once etc. that things like cloud sharing just don't work for if it's a every once in a while type of file sharing etc. E-mail is one of the best ways to send things to people quickly and easily--especially multiple people at once.
People just come from different view points as well. I'm a PC user and always will be. I prefer file systems and things they way they are. I'm not the typical Apple fan that embraces changes. I'm more of a stuck in my ways guy who'd rather just do things the way I know how than to have to adapt my work flow and learn new things.
So I just don't currently bother doing much work-related tasks on the iPad as I just find most things easier to just do on my PC. I've integrated a few things like taking short meeting notes on it and sending it to Evernote, ditching my old palm pilot and using Google Calendar and synching that to the iPad calendar, put my library of PDFs of research articles into Goodreader so I have them all on one device and can reference them when writing articles etc.
But other things like document creating, sending work e-mails, working on data and data analysis etc. just can't be done at all or can't be done in a manner that's easy enough for me to bother doing it on the iPad when I can do it on my PC with less hassle.
And I'd like a tablet that was a few steps more toward a PC (but not a full PC OS by any means) so I could at least get by with only taking the nice and light tablet on the road vs. having to take a heavy laptop (again, I don't travel often enough to buy a 2nd, more portable laptop that I'd never use at home).
Others like new tech, like figuring out new ways to do things and are more willing to jump through hoops and deal with learning curves while adjusting their workflow to new gadgets. More power to them, but that's just not me. I like my iPad, but mainly as a media consumption task, with some work related reading (I don't like doing revisions or mark up on it much, unlike the poster above--easier on a printout or the PC for me), note taking etc. mixed in. But ideally I'd prefer to move onto a tablet that was a bit more work functional for me down the road, so I'm hoping MS hits a home run with their Tablet OS in a year or two.