Update: Ubuntu 11.04 seems a good improvement over the previous one. Read my adventures here installing it on the same laptop.
The HP ProBook 4720s is what you’d call a business workhorse: metal casing, fast WLAN, 6 hours+ battery duration, a Core 3 and a matte (anti glare) 1600×900 LCD screen for a fair price that comes preinstalled with 3 GB (2 + 1) RAM. I just spent my allowance on another 4 GB of RAM only to find out, that my HP 4720s had only a 32bit Windows 7 installed – so 3 GB wasted out of the total 6 GB now installed. Since I’m mostly programming and surfing the net with this HP, I can’t go wrong with a Linux distro (or so they say  ), so I picked an Ubuntu 10.10 64 bit Desktop edition. In the end, everything worked either straight away or after some tweaking:
[x] SD Card
[x] Touchpad (reduced functionality)
[x] Hotkeys (sound, brightness)
[x] Screen brightness
[x] Internal microphone
Things that, so far, I couldn’t get running:
[ ] External microphone (line in)
[?] External screen (untested)
After downloading and installing on a USB stick it boots quite fast and gets down to business.
Obstacle 1: no WLAN during installation
It turns out that, unfortunately, Ubuntu doesn’t fully cooperate with the Ralink RT3090 WLAN chip – I didnt fix that during the installation but afterwards. In my first take, I tried to install the OS on an 8GB class 10 SD card, which not only took forever (more than an hour), but also booting from the SD card (yes! the HP can do that) was surprisingly slow. Thus, in a second attempt, the Ubuntu was installed on the 320 GB Harddisk.
Obstacle 2: no WLAN after installation
The WLAN woes lasted past the installation phase and several package updates didn’t fix the problem either. This is apparently a known issue related to 64 bit with a couple of workarounds , . I tried the solution offered in , comment 16 which at first crashed the laptop. After a reboot however the WLAN works (almost) nicely, with some rare disconnects.
[Update 2010.01.30] The WLAN is unusable during high workloads and keeps disconnecting. The following sequence of steps seems so far the ultimate solution:
1. Follow the instructions in . This will install the Ralink rt2x00 drivers which apparently also work for the rt3090. However these cause an unstable WLAN.
2. As per  you should add
3. Contrary to what  claims, I had to blacklist the rt2860sta driver in /etc/modprobe.d/blacklist.conf, meaning that the only line related to ralink modules is:
4. After rebooting the keyboard Wifi LED was blinking indicating WLAN activity which I disabled by following the instructions in  by adding to /etc/modprobe.d/wlan.conf:
options iwlcore led_mode=1
[Update 2011.02.06] Can’t get WIFI to work on channels 12 and 13
Obstacle 3: no right-click with touchpad
The last, and yet unsolved, problem remains the missing right-click functionality of the integrated touchpad. While in terms of sensitivity, speed and accuracy (even edge scrolling works) little is left to be desired, I couldn’t get right clicking to work. While  (see comments) suggests this fix:
echo options psmouse proto=exps > /etc/modprobe.d/psmouse.modprobe
the side effects include a disabled edge scrolling and very low pointer speed which, at least for me, is grave enough to disqualify it. If you tried it and want the old setting back: just empty the contents of psmouse.modprobe and reboot.
[Update 2011.01.25] A strange thing seems to be going on: while right clicking doesn’t work, right tapping seems to be possible when executed with diligence. To get it working, one has to exert the right amount of pressure (it’s more than you’d use for a regular tap) at the very bottom right edge with precision and quite some speed. I’m using the following script executed at startup which reconfigures the synaptics driver to allow for easier clicking which resizes the clickable area and increases click timeouts:
 HP ProBook 4720s Linux drivers
 Ralink Linux drivers
 Linux checklist for HP ProBook 4720s
 Ralink 3090 wifi connect problems in 10.10 64 bit
 Bug 659143
 Ralink 3090 wifi connect problems in 10.10 64bit
 Stop anoying blinking wifi led
 X Updates for ubuntu