I'm lazy so my responses will be inline...

Quick comment: There's a lot of stuff you can do with this thing (it's a small computer), so you'll probably want to get used to using the Google search bar on this site and browsing the wiki. maemo.org has a browseable app repo.

i just recently sold my iPhone (4gb) for 400$ (!!) and then bought N810 for 360$. so far loving it, but i have a couple of questions..

1st: how to become root in terminal?
If you're geeky, you might want to install ssh in addition to becomeroot (ssh asks for the root pass on install)

2nd: does the load applet slow down he system? seems like it.. a bit..
Not sure. Wouldn't surprise me.

3rd: is there a program that will automatically lock my device when i close it?
There are a variety of programs that allow configuration to hardware events. I think there's one app that lets you put your finger over the light detector (not sure what that's called) for a few seconds to lock.

4th: why is the web browser so slow..?
A 400mhz cpu with 128mb RAM? There is a beta mobile firefox, but you'll be less impressed with that.

5th: what is boingo?
Already answered.

6th: i don't get how to manually give the IP settings to the connection manager.. say, if i don't have DHCP on my WiFi router.
If you edit a connection, the last screen in the wizard has an advanced link.

7th: is it true that the more apps i install the slower the system gets?
Not that I've seen. Any app that runs a daemon will slow it down though.

8th: i still couldn't get GPS working well in Maemo mapper..
Make sure you select bluetooth and leave the path blank. Upgrading to the latest maemo release (Diablo) has helped a lot, but still takes a few minutes

9th: is there a Maemo version of liquid wars?
Doubt it.. if it's not in games.

10th: is there a nicer email client for n810? for example, i loved the one in iPhone.
Haven't looked in to e-mail, etc, but I doubt you'll find anything like what's on the iPhone any time soon.

11th: in the default chat program, in GTalk, is there a way to show the whole status of a person?
Not sure. I've only used pidgin on the n810, but I was under the impression it uses Pidgin libs for a lot of the work so it's probably possible, although it may require code changes

more questions coming!

thanks if you answer any, or if you don't.