Personally, I can't get over the fact that I'm using the exact same Vim text editor on my N900 that I use for all my work on my desktop machines. Not a crippled version, or an app that kind of looks like Vim, but the real deal. That, along with the fact that I can squeeze 80 columns of text onto the screen and still read it easily, means I can work with serious documents and source code files without any trouble. I'm certainly writing more with my N900 that I'd ever expected I would with a cell-phone-sized device.
I'm not sure there's a much simpler way than to use the usb cable. Also, I connect to my Mac over bluetooth without needing any third party applications; that works quite simply as well.
Well, odds are the N900 will pretty much be the last of its kind to come out of Nokia. Android phones really don't give you the same kind of options you have with Maemo (unless you hack them to do so), and of course iOS and WP7 are essentially useless except as containers for pointless little apps. (Maybe I'm being a little harsh, but my previous phone was an iPhone; I enjoyed playing with it for a while after I got it, but eventually I just ended up doing nothing more with it than answering phone calls. I just don't have time to sit and watch teensy tiny pretty little apps doing teensy tiny pointless little things.)
In short, the future may look bleak for the N900, but there's not a lot of competing products that can do what it does. I think it's still worth far more than the competitors.