In my experience, there's a relationship something like so:

Where...
w = [likelyhood of something going wrong]
k = [how much you know what you're doing]
s = [how little risks you take when dealing with thing you don't understand]
r = [random shitty luck factor]
...then:
w = (k-s)r

Obviously I'm just pulling this out of my ***, but most of the time, unless you got a shitty hardware batch that is either incompatible with the fancy uboot patches e-yes and matan implemented, or has a crappy usb port, the rest seems to more or less be dependent on the doing stupid ****, and how much you know about said stupid ****.

For instance, my N900 lately developed an instability where it crashes when I'm trying to use PgUp/PgDown/Home/End in combination with Shift to select large amounts of text (wait... how many phones let me map PgUp, PgDown, Home, and End, to my keyboard, without giving up any other keys already mapped to it...? Maybe something with WebOS? Android? I should hope so.) But do I ***** and moan at the phone? I get a little bit frustrated with it, yes, but the more I have observed the problem the more I realize it either has to do with some of the kernel parameter tweaks I've made, or some very rare bug exposed by CSSU installation - and I am getting pretty certain I've ruled out CSSU as of today.

As for overclocking, when overclocking to 1000MHz didn't fix your problems, that should've told you something: the problem isn't the CPU. (Speaking of which, folks, don't go encouraging the guy to not reveal that he overclocked the CPU - selling it without admitting that is just screwing over the guy who buys it, at least he's being honest.)

It's widely known the primary slowness problems on the N900 are I/O bottlenecks. At 600MHz the phone, clean out of the box, runs like 30 programs without slowing down. It's when you cram it with more and more crap, some of which fills ram and cpu cycles in the background, that everything starts slowing down. Yes, other phones don't have this problem, but other phones also benefit from a more diligently reinforced Q&A process, where-as here we have Extras/Testing/Devel, yet most people just go straight to Devel, and I wouldn't really blame them for it either, because Devel has like 25% of all the good stuff (and just three months ago, I would've estimated 50% of all the good stuff; when I got my N900, I would've said you have to go to devel to get proper functionality out of the phone, because that's how much was still in devel only).

But the point is, the phone isn't the problem. The problem is that just like a Windows box won't stop you from installing a program that blue-screens you upon running, nor will the N900.

As I've said plenty of times on here, if even one of the other phone OSs out there allowed you the freedom this one does, people would grind those to the point of being "Is so poor at multitasking that I can't answer the phone when it rings". The various companies who make those OSs chose to clamp down on your freedom so that they don't have to listen to all this irrational *****ing - the N900, mostly, doesn't - you're welcome. (Which is also why just reading "sucks at multitasking" in a criticism of the N900 probably makes people respond the way they do you your posts. Guess what, if I run a virus scanner and a virtual machine on the same Windows laptop, even the dual-core, 2.something GHz machines that are so common today will grind to a slowness untolerable. Does Windows and said laptop suddenly suck at multitasking?)

*Shrug* At the end of the day, not every phone is for everyone, so I wish you luck and more happiness with whatever else you get. But your post shows that you didn't know how to even begin to get the most out of the N900.

- Edit -

To be fair, given what was posted since I started typing, it is possible you're in one of those rare exceptions where random luck screws you over regardless of what you do, and it really may have been a faulty N900.