[How long does a linden sell usually take to process?]

If we are talking about the LL Lindex exchange the $L to $US should go through right away. After that you need to either withdraw to paypal (takes 1-5 days) or use a wire transfer that takes about 15 days.

Personally I use https://www.virwox.com/ the paypall withdrawal usually goes through instantly, and there are a lot of other options you don't get with Lindex.

[Help with disappearing necklaces?]

Sounds like the nano prims on your necklace are derezing due to LOD (Level Of Detail) factor. 

Try this...

 

1. Show the “Advanced” menu with Ctrl-Alt-D, or Opt-Ctrl-D on a Mac.

2. Select “debug settings” near the bottom.

3. In the blank space, copy and paste the word:

RenderVolumeLODFactor

Default in most viewers is 2.0 change it up to 4.0

[Why has Linden Labs not put out a better viewer, so we don't have to resort to using other viewers?]

What you have to remember about the official 2.x viewer is that it is designed more to make it easy on new and or casual residents with average computers. However if you rent, build, run events, have a store etc. you now have new hoops to jump through to get anything done. Not to mention of course the overall interface is so different from the classic one that most older players just hate it.  Now everyones idea of a "better viewer" is going to be different, so I would hate to see LL waste their time doing a dozen variations.

Of course the cool thing is that we do have different 3rd party options that all meet different needs. (something I have never seen for any other virtual world)