Hi all,

After reading about all these woes and experiencing it myself, I have done some further experimenting in order to isolate the problem and as a result I have found a very EASY WORKAROUND which in no way impacts on your computer.

MY SETUP:
Hardware:  HP 2133 Mini-note netbook computer
Fresh install of Ubuntu 9.04
Using internal wireless modem with Broadcom STA driver for wifi access

PROBLEM:
After booting up and providing relevant information and password I can connect wirelessly.
If I leave the PC for a while and return then I find that the wireless connection is down and there is no way I can get it up again except rebooting, very inconvenient.
This problem did NOT exist in Ubuntu 8.10.

ACTIONS:
I searched the Ubuntu Forum and discovered that many, many others reported a similar or identical problem on many differenct hardware platforms.
Some had discovered that if they closed their laptop computer which switched off the screen, then they were immediately disconnected from the network and needed to reboot to get back on again.
Some therefore were pointing to the openchrome graphics driver (I find it amazing that a graphics driver should somehow interfere with the wireless driver).
So, the general consensus was developing that it had to do with the openchrome video driver and suggestions were to fall back to the vesa driver. I tried that and it did indeed prevent the problem form occuring, so further pointed a finger at openchrome.

I rebooted with openchrome again and then experimented this way:
I opened 
System/Preferences/Screensaver/Power Management
 and set it as follows:
"Put display to sleep when inactive for" and set it to "2 minutes".
I waited 2 minutes, the screen blanked without closing the laptop lid.
I woke it up by moving the mouse and tried if I still had a wireless connection up - NO - wireless connection was DOWN.

WORKAROUND:
I rebooted and again opened
System/Preferences/Screensaver/Power Management
 and set it as follows:
"Put display to sleep when inactive for" and set it to "never".
Now the wifi connection stays UP, it has not gone down even once!!!

But when I leave the machine I would like it to blank the screen after, say, 5 minutes.
So I simply set the "Screensaver theme" to "Blank screen" after 5 minutes, and the screen blanks but when I move the mouse and check my wireless connection the it is still UP and running!!!

Andrew Aylett sent me this link (thanks, Andy):
http://www.openchrome.org/trac/ticket/288
If you go there you will see there is a patch made available for the openchrome driver and at least one HP2133 user has tested it and reports that it has fixed the problem.
My problem is, I don't know how to apply such a patch and since my computer now stays connected, I am not very keen to experiment with it.
What I am hoping is that one of the clever Ubuntu system guys will make the patch available for all of us to download and install the usual way via synaptic or one of the other update managers after rigorous testing.

This is the kind of problem I find extremely frustrating and if newbies have this problem, then it might likely turn them off Ubuntu and perhaps Linux in general. This problem was reported by Ben McCann in February and perhaps by others too that early and here we are now in May and the problem has not been fixed. Is that good enough? Well, I have been a applications project manager for about 25 year and I would not have accepted this situation. Anyway, now we know where the problem lies, so please let us have a fix for it.