The N900 is a very dated device by today's standard, not only hardware-wise, but software-wise as well.

MicroB (the web browser of the N900) is more than 5 years old and it shows - it's based on Firefox 3 (which was a memory hog, especially compared to today's Chromium).

• Has a slow/outdated (and thus incompatible with the modern web) javascript interpreter, which takes ages to process scripts and it will bring the weak CPU down to it's knees.
• It has a tendency to crash your entire device (low RAM means the slow eMMC (N900's 32GB storage) is used as extra RAM, which completely destroys all I/O because the qeues for memory access take too long to process).

A possible solution to this problem would be running regular Debian in a chroot so you can run Chromium, except...

• Low amount of RAM etc. -> See the text above.
• Limited to Debian Squeeze (which is now oldstable and it will soon be obsolete) because Wheezy doesn't run on the N900.

The few apps out there are all pretty high quality stuff and they run great, but there are almost 0 service-specific apps (no Google Drive, <INSERT YOUR CARRIER APP>, Parkmobile).

Hardware faults/dated components.

• Low resolution/brightness screen.
• USB port can get loose.
• Keymats wear down over time.
• Solder balls get cracks.
• SIM slot can break.

Despite all this, I love it to death.
Honestly, the main reason people get the device these days is either because they lost their old one (meaning they were already long-time fans of the N900) or for the qwerty keyboard.
I cannot recommend it to anyone these days, especially someone who's "spoiled" (don't mean to offend you) by the Android ecosystem & hardware.

If you really want a small gadget to mess around with, just get yourself a Acer C720/second hand Thinkpad.
Or wait for the Pyra if you want something a little more portable