My wife and I each own an LG Optimus phone and after much trial and error I have discovered a few things that I hope will help others make these phones workable.
First off, I don't believe these are bad phones. Hardware-wise they are on the lower end of the spectrum of Android phones, but they are a nice small size and with the PROPER SOFTWARE they are adequately fast for daily non-gaming use and can be made to work really well.
Out of the box, these phones suffer from several major issues. Most were compounded by the recent 2.3 update so I strongly recommend downgrading to 2.2 if you have not already before doing anything else.
SLOWNESS/FREEZING/Rebooting by itself
Inability to answer a call, unable to unlock the screen, sluggish response, restarting by itself etc. After a fair amount of testing I have discovered that these issues can nearly eliminated by doing 2 things.
Switching to the free version of LAUNCHER PRO
Using the 'CLEAN' Sprint ID or removing it all together (details can be found on google)
Unable to charge even with the AC Adapter
It seems the 2.3 update actually modifies something in the hardware of the phone such that even after reverting to 2.2, some phones (my wifes for instance) will still not charge with the factory LG wall charger.
Purchase a higher MAH wall charger. The Motorola SPN5504/SKN5004A micro-USB Home and Travel Charger is $5 on Amazon.
Works perfectly and will solve this issue.
SD CARD UNMOUNTED
Using a quality SD card (I'm using a SANDISK currently) and running 2.2
If the problem persists, try another (new) card. I have tested 4 different cards in our phones and I had the issue return with 1 other aftermarket card. Currently for my wife and I this problem has not returned.
One other thing I have learned, the Facebook app can really makes this sluggish at times. Both my wife and I have tested using the phone for a week with and without it and there is a pretty clearcut difference in terms of battery life, overall performance and reliablity when that app is not on the phone.
I hope this info helps other LG Optimus owners deal with the hand we've been dealt.