This is a topic I'm trying to weigh out as well. I have been watching Craigslist and ebay, and the old manual focus lenses are a lot cheaper, but I'm still leaning towards saving up for that $200 Pentax smc DA 50-200mm F4-5.6 ED Lens (copied from the website... I dont know what half of those numbers mean!!!

)
The reason is that "pentax says this lens is made for my camera". Does that mean its the only choice? No. I'm sure there are other choices. I'm wondering if this particular lens will weigh a lot less since the K-x is so light and the older cameras were a lot heavier.

I'm also still undecided about this lens because I really only wanted to get ONE extra lens (for now) and I was thinking a 300 would be better. Not sure why really. So... before I make myself sound any more newbie than I already have...

How about a couple of all-out PRO / CON reviews???
New may be lighter?

Is it cheaper made? More to break?
An example: (just stick with me... I'm trying to make a point...)
In home audio and car audio you want OLD equipment. I'm still running 1980s car amps in all my vehicles. They are rated at 25 watts per channel (Orion HCCA 225 hand made in USA) They will flat out DESTROY these new 2000 watt amps that are mass-made today in China. They also (obviously) last longer and can take more abuse. Are lenses the same principle?
In home audio, I run a newer Onkyo 6.1 receiver, because the older stuff don't have the processing effects for surround sound. The older stuff brings TOP DOLLAR (why I sell so much of it on CL) but those buying it are DJs, and old school people who want to jam out to Zepplin and the Beatles.

The sound on the old stuff is a different tone rich sound that some people love. Is the same principles that apply to audio equipment the same principles that apply to camera lenses?
If so maybe I should go get that K-1000 at Megathrift with the 200mm Tamron lens in the old leather tube for $100.
So those of you who know more about this than those of us who don't... Can we get some pros and cons? A sort of way to decide which way to go?