Just a word of warning: unless skype and/or internet radio is a high priority for you, DO NOT go beyond m33 3.71! Apparently sony has changed the memory stick driver in 3.80 and above to an inferior version which
does not play nice with 3rd party brand sticks, notably sandisk. There have been many reports of games and/or saves no longer loading properly under the new driver where they were fine before. Dark alex has come up with a semi workaround by a patch which shoehorns his 3.71 driver back into the new firmware, but the process is too complicated for most casual users imo (and there are many reports of bricking as well).
Sadly i updated to m33 3.90 before knowing about this, and all my memsticks (sandisk 4 gig and 8 gig) have been affected. I can't run patapon for example, and emulators run noticeably slower than before.

Thankfully the older games still work (though again noticeably slower). Just wanted to make sure you guys were aware before updating. If you don't need to, i strongly recommend you wait until this problem is resolved.