I still use my n900 for a few reasons:
1) Most of the time I'm some place that as free wifi. The n900 combined with TOR and LocalPhone mean I basically have a free cell phone. The few times that I NEED a phone with me I have a cheap pre-paid phone that usually ends up costing me about $5/mo through Verizon.

2) The fact the it's the only smart phone (that I'm aware of) that has Rockbox. Once you get Rockbox customized no other music player comes close. Managing a library of currently 7251 songs coming in at 27GB would be a nightmare in anything else on a smart phone.

3) nmap, aircrack-ng, wireshark, and other fun tools.

4) TRUE GNU/Linux environment, I've tried rooted android devices, but busybox just doesn't do it for me. My job revolves around Linux, being able to scp files from or to my phone, or worst case piping data through nc and gpg2, are things that are hard or impossible on another device.

5) And finally, I paid something like $550 for it new, and it's going to give me atleast another 6 years even if I have to hot-glue and duct-tape it together.

I've yet to encounter the broken USB port so many others have, so far I am crossing my fingers. Battery life has been the thing I'm more disappointed it, I've been considering building a dual battery.