PSP Firmware 6.20 is live, now available over the network update and also downloadable below. We now have a new comic reader built into the firmware and a new TV bar in the XMB.
Here’s the changelog, taken from the Playstation Blog:

Digital Comics Reader – PlayStation Network Digital Comics is a new service launching in [...]

Ok so apparently, PSP Firmware 6.20 is on the way. Tomorrow infact. It will include a new comic book reader that will go with the launch of new comic book service available over PSN. So where is this info coming from? From the horse’s mouth at the Tokyo game show, claims this blog
The new comics [...]

Sony’s answer to the PSP game decrypter release perhaps? Maybe its patched, but the update seems to be more geared towards the PSP Go and its launch.
Firmware 6.10 will improve compatibility with Media Go and all PSP titles. Plus there is now a new music application called sensMe, which basically automatically categorizes your music collections. [...]

As predicted today Sony released PSP Firmware 6.00 which now includes updates specific to the PSP Go which is set to be released in October. While I was looking around at exactly what’s new in Firmware 6.00 there is nothing too special too report. There are a few new theme colors and really that’s about [...]

PSP Firmware 6.00 has just recently been released to PSP developer’s, for the testing on PSP tool units and development kits for future PSP releases. It certainly seems firmware 5.55 and firmware 5.70 were simply releases to thwart further security bypasses / exploits, like the recent MOHH Exploit.
Since Sony have released this firmware 6 [...]

PSPGen have spotted the PSP Go on display sporting Firmware 5.70. So this could be the firmware the PSP Go might ship with. This video also shows us some of firmware 5.70, however its in French…
Source: PSPGen

Some news via the Dark_AleX forums as users have discovered that G.I. Joe: The Rise of Cobra, needs firmware 5.55 in order to run and is included on the disk. While PSP Firmware 5.55 hasn’t been released yet (if ever) via the network update. Its unknown what changes are present in this firmware. But its [...]

Sony have posted on their offical blog that the release of Firmware 5.50 is due tomorrow. While its releasing a couple of big new features. No doubt its come out sooner rather than later to patch up the recent TIFF Exploit found. Users wanting to take advantage of the TIFF Exploit might want to advoid [...]

Sony have released Official PSP Firmware 5.03,well we have no comments on exactly what this does. It seems there are no updates or added features other than to fix a security vulnerability found in the latest PSP system software revision? Hmmm that sounds like they have patched the Gripshift savegame exploit / hack for the [...]

Sony were quick to release a bug fix firmware update for the PSP. Firmware 5.01 fixes the previously posted issue where downloads from the PSP store would state you didn’t have sufficient memory space if you had a 8gb or 16gb memory stick inserted.
This download is available via the network update from your PSP [...]

Users of larger memory sticks may notice that you couldn’t download content due to an error stating insufficient space. 5.01 will fix that problem.
Here’s what Eric Lempel of PSN had to say:
PSP firmware update 5.00 added direct access to the PlayStation Store, and we’ve since found an issue related to larger-capacity Memory Stick PRO Duos, [...]

As planned Sony have released PSP Firmware 5.0 via the network update feature or download below. Release changes:

* The [PlayStation Network] category has been added, and [PlayStation Store] is now available under this category.
* The sleep timer feature can now be used under [Music]
* The system will automatically change to USB mode when a USB [...]

Sony have released PSP Firmware 4.05. Don’t get excited its nothing special…. Just some new music player visual effects. Heres the huge changelog:

* New effects have been added to the visual player under [Music"].

I guess Divx support was and will always be just a rumor.

Sony have released PSP Firmware 4.01, this minor update includes the following:

Display of search results under Internet Search has been improved for certain languages.
Playback of video content under Video has been improved for certain file types.

Playback has been improved for certain file types? Does this mean DivX ?
Download Via network update or here -> PSP [...]

PSP Firmware 4.00 has been released by Sony. This slighty lack lustre release features the new internet search feature via google and the ability to control the view speed of videos on the memory stick! Wow I hear you say…. Not much of a release for a x.00 step up in Firmware.
* [Internet Search"] has [...]

Sony have posted on thier blog that PSP firmware 4.00 will be released soon. While there are some new features, nothing major has been added like the much wanted DivX support. Oh well I guess next release? Fingers crossed, come on Sony its what were after! Question is will M33 / Dark_AleX be releasing 4.00 [...]

Sony have now released PSP Firmware 3.95. This update is available over the network update feature in your PSP’s XMB or download from this link here -> PSP Firmware 3.95

* While playing PSone games on your PSP, you can now customize how the buttons are assigned by going to [Controller Settings"] > [Assign Buttons"] and [...]

Posted on the PLaystation blog is an entry about the next firmware. The updates seem almost as minor to me as 3.93 was. I’m expecting most people to not even bother to update.
So now you can:

customize the controls when playing PSOne games
quit Remote play then choose whether or not to leave the PS3 powered on.

Though [...]