Mine is a 2104, it was bought on a JR store in New York around july

edit: just to confirm, yes, that is not a typo: two-one-zero-four

Nokia RX-51, 2101 bought from Nokia Flagship NYC first week it came out.

I think the more important issue we should be looking at here is trying to find the differences. There's some known hardware issues with the N900 so I will tell you bout my hardware experience;

(Current config; PR1.3, Titan Power45 @ 500MHz-1150MHz)

-All paint on keys is still there, not a scratch, I use my fingernails to type a lot of the time.
-USB port holding steady just fine, it has dropped off my night stand and dangled numerous times from the USB port.
-Silder works just as good as when I first got it.
-OCed at 850MHz for 2 moths and 1150MHz for 5+ months - no crashes, no bugs, nothing.
-Never had a random reboot.
-I did have a dead pixel once, but it appears to have fixed it's self because the screen is once again flawless.

2104

Gets unstable with OC, even worse with OC+Under Voltage
Green vigneting with the front camera even with Skype (if you want i can post a picture)
A tiny ( <1 milimeter diameter) pit has formed on the screen
The rigght arrow key developed a "hole" about 3 milimeters wide in the black stuff, i can see thru the hole but i can't feel it (perhaps it is on the underside of the key?)
Have had rare random reboots.
The USB plug is a bit wiggly but so far seems to still be attached and fully functional.
Usually i get an average of 6-7 hours of battery life, more if i'm not touching it.
Updating to power45 i at first had a difficulty booting up reliably, but seems it is better now.

Hm, what else would be relevant?

how do you check the version?

mine is 2204...it was a replacement i recieved from nokia service center because my original that i got back in DEC 09 from nokia was defective usb

A lot of people have issues with the sliding mechanism. Do you have any?

My 2101 hardware example had two bright points in my LCD. When the screen ceased to function at all (totally black, no sign of anything being written to the screen) I sent it in to NokiaUSA repair point. Came back with very sweet looking screen without the bright points. That was five or six weeks ago and there is no sign of them returning.

I use the Nokia case now. Previously, with the old screen, I used a case with magnetic closures and I have to wonder if they contributed in some way to the spots.
Other observations:

• - preordered from Buy.com in October, received in December week 48 build
• - rock solid oc'd to 1100MHz
• - blue paint flaked off arrow on first use of key; now flaked off on the 9
• - USB appears solid but not as solid as it did 11 months ago.
• -slider mechanism is still solid but again, not as solid as it was 11 months ago.

2101 rock solid.

no dead pix. not a scratch on the keybord. no issue with usb-port. no issues sliding mechanism. droped 3 times in the floor. always land screen down. not a scratch. bought this rock dec 09 from nokia.

2101,
Except for once bricking my phone (I think because I killed bme's configuration, since nokia claimed all they did was a reflash and it started working, for me it wouldn't respond to any usb cable connection, from PC or power),
everything is working solid, keys are a little scratched but I am using a game gripper, and I do notice that the slider is, barely, touching the keys. No USB problems even though it fell connected to the cable a couple of times.

CZ - Czech Republic

I have two N900 from februar 2010

first 2101,second 2104

-Never had a random reboot.
-All paint on keys is still there, not a scratch.
-USB port holding steady just fine.
-Silder works just as good as when I first got it.