I got my 9500 from my dad last year. It was a 180MP but it did have a Sonnet G3 400MHz upgrade in it. I added a Radeon7000 and MacPicasso860(yumm... !3D override! ) and upgraded the RAM to 704MB (interleaved).
I put in the ZIF Carrier with a B&W 350MHz G3 I had laying around, OC´d it to 413MHz and pushed the bus to 59MHz. It ran stable even with interleaved RAM! - but only with some extra cooling. I added two 80mm fans for RAM cooling, a 60mm fan to CPU heatsink and a heatsink to the RAM controller. The baby was incredible loud and didn´t fit its case. I tried a big PC case but was not able to fit all the guts inside.
I used the 9500 mainly for OS9 gaming.OSX10.3.9 did work very well but did not shut down properly.
Later I downgraded everything except the RAM and gave it back to my dad cause he needed it for work.
-got a G3MT instead -

I bought mine, the first full tower (and Old World Power) Mac that I had owned, in mid-2003. It came from a pre-press company, and its price of AUD200 (which was my offer, not their asking) now seems over-generous. Its RAM complement (144MB) and processor speed (132MHz) were miserable, but it had a Radius ThunderColor 30/1600 video card (natch, given its previous use), and was in excellent cosmetic condition.

I replaced the RAM, eventually reaching 1024MB, which was distinct overkill, and certainly got VM's knickers into a knot until I assigned enough RAM to cache to pacify VM. Even then I rarely use VM in any machine unless I am forced to do so. With a MAXpowr G3/400MHz daughter card and new logic board (both NOS), 24x CD-ROM drive, 2 x IBM 9GB and 1 x IBM 18GB 68-pin HDDs, Adaptec 2940U2W, combo FireWire/USB card, ATI Rage Pro and AsantéFAST NIC, and running OS 9.1 it drove a 17-in. Studio display. Now that I have taken apart and upgraded 50-odd x500 towers of that design I have to consider the task just plain tedious rather than a pain. I have more reservation about the design and plastics of the front pressswitch, removing and replacing which is always fraught with risk of breaking the retaining tangs.

The 9500 was a valuable member of my LAN for three years, as backup for the System installations, and download/distributor for the new software, for a dozen or more 68K Macs, as well as being my principal OS 9 machine when I put the iMacs under OS X at the end of 2004. Gotta love the Studio Display for wave editing of sound. Then I acquired an 8600/200 in mid 2006. As a 9600/400 now, that Mac wears much of the goodies from the 9500, which is at the moment, like an actor, 'resting' between engagements.

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The 8500/9500 case is the worst for upgrading. When I'm ready, I am going to gather all the parts needed to max mine out, open it up once, then never open it again. I have an 8600/250 and two beige G3's and they are the nicest old world Macs to work on. The G3/7500/7300/7600/7200 desktop case is also nice.

I'll add my configuration to the list. Bought this 9500 off eBay for $40 about 2 years ago. Came with a G4-800 card, 960MB of FPM RAM, a couple of HD's, an external CD burner, an external DAT drive that I can't find drivers for, and two extended keyboards, one of which was unused in original packaging.
It now has a pair of 15K RPM HD's, an 18GB Hitachi and a 36GB Seagate, Rage 128 and Voodoo 3Dfx video cards driving a pair of LCD monitors, 10/100 Ethernet card, and an Adaptec 2940UW card driving the HD's.
It's a very fast OS 9.2.2 box but does have a couple of annoying glitches.

I agree with everyone else that the case is horrible to work on; you have to virtually disassemble the machine to change the Pram battery or add Ram.