I don't think you really want to enable R&D mode. Just download gainroot or openssh so you can get root access to your device. R&D mode is a bit of an anachronism from the "old days".

As qole said, the question to ask isn't "How?" but "Why?"

You may think you want it enabled, but I can assure you with near-certainty that you don't.

rootsh is actually it these days.

Agree... I would like to see a "its whatever you want" approach to the market where they show an example of how different users will use it.

I think there's still a market for hard keys in phones. But everyone seems to think that everyone wants soft keyboards (which alot of people have accused the smartphones especially Android hardware makers of).

I want to vote for 3 options: the open-source community, techies, and mobile device "power users". Mass market, not yet. Maybe in later stage though. Reason: platform too young (in the 5.0 sense), software must adapt (to compete with other platforms), price too high (in that sense iPhone or Palm Pre are not for 'mass market' either; we need more Maemo devices for different target groups ).

No way everyone is thinking that. Heck, there is also still a market for non-touchscreen phones. Each have their place. More important question is: how much market place. Now that is difficult to answer.

Current soft keyboards have advantage of easily remapping. OLED based hardware keyboards have this advantage too, but are too expensive, and the number of keys is still static. I can see these initially being used for hot-keys (like home/email/contacts/agenda), but otherwise... price, for now.

That is one disadvantage of hardware keyboard: localisation. Inflexible to change during usage with change reflecting and lowers reselling value while inflexible to buy from other countries due to hardware keyboard (unless user not care). Now, afaik you could change the hardware keyboard of N810. At least you can with many laptops. But I don't know about N900...?

Why I like hardware keyboard: I like to feel my keyboard, feel the hardware keys. I like the tactic feedback of a hardware keyboard (especially the old IBM keyboards). I like that a hardware keyboard is static, it never overlaps the screen changing the usable resolution of the screen. The screen doesn't become dirty either from typing. The number of mistakes made during typing is considerably smaller than on touchscreen (yes, I do compare with my iPod touch).

All versions AFAIK. You can freely download a flasher (Linux, Windows), enable R&D mode using a setting. Been like that forever I personally avoid R&D mode and just use 'rootsh' package to get sudo gainroot.

But don't you get those cool debug (info) messages on boot?
OK so I'm just a geek at heart ;-)

Gotta admit I have only quickly browsed the dev docs, but I'll be missing the debug data soon enough anyway, so I don't really see very much point in first customizing it to my liking and THEN flashing it....

If you just want to gain root access, then R&D mode is not really what you want. R&D mode has several other side-effects that may not be desirable for regular use. E.g. in R&D mode, just shortly pressing the power button switches the device on immediately.
R&D mode has been available in every NIT, and can be enabled with the Linux flasher utility.

I have never used Linux, so the question I should've asked is what is R&D Mode, what is it used for, why would I use it, why does everyone say I don't want to use it (how do you know??), what is "root access" (I sort of understand that one, but wanted an "expert's explanation. sdskeeps gave some insight.), and how do I use it?