I just upgraded to 4 on my SD and thought that was the limit.
You were able to successfully upgrade to 8? Interesting. 
Anyways..I have had very little problems with mine.
No noices like the one person mentioning above.
To get information out of my Micro SD card obviously I do not pluging the phone to my computer, I have an micro sd card reader. Works like a charm.
Anyways...sometimes I do think that the battery should last a little longer but hey whatever.
GPS works like a charm. I was traveling from Florida to New York and used my GPS and it worked like a charm!!!
It even told me if there was heavy traffic so it diverted me from it and took me back to the same parkway after having passed the deadlock. I am very happy with this phone.
Now if I only could get my Optonline email to work would be nice. 