My advice? Ignore them. Unless you are certain they know what they are talking about, assume they know nothing about their N900. Grass is always greener on the other side and when people start talking about their own lawn to others, it´s always the greenest grass ever seen on earth and in their garden the sun always shines.

If you have been playing a lot, especially with low-level settings and your device seems to lag constantly, I would really, really start with a reflash. Bringing back your device to factory-state, or at least as far as possible, allows you to start with a clean slate.

After that, apply patches and tweaks manually. Do them one by one. Make sure you test them. Give yourself time to see and learn. If you know things are good, get on to your next tweak.

I would stay far, far away from scripts like the one that you linked, especially if you don´t fully understand what these scripts do.

Lastly, I document all the tweaks I do.

Yes and no, I´d say. First: You don´t want to reflash every week, so be carefull with the tweaks you apply. But even with the default backup program that comes with your machine, you should be able to restore quite a few settings.

Make sure you have a minimal list of all the programs you want installed after reflash. Remove all others that you don´t find absolutely vital for a clean machine, and once you´ve done that make a backup. Be sure to save settings and installed programs as well. Move your backup from the n900 to your desktop machine and restore it after the reflash. Presto.

* Please, be aware that the longer the list of programs, the bigger your chance of recreating the lag that caused you to flash in the first place.