Here's my list of what works and what doesn't (so far) in:
DP6.02 in 10.6.1 on an Intel machine (early 2008 8-core MacPro):
First the good: Almost all plug-ins work better, MUCH better, i.e. more responsive controls, quicker and smoother when switching plugs on the fly during looping etc. So far even the ones that aren't 'officially' SL proof (EW Play, Omnisphere, etc.) work just fine or even better than before.
Now, just to be clear, these plugs are all updated to their newest versions and run inside this very combination DP6.02, 10.6.1 and MacPro 8core.. So making no claims how this all works in Logic 9 or something... also, I turned pre-rendering OFF for all plugs in DP6
What broke?
Stillwell/Schwa plugs are not working yet in SnowLeo as most of us know, and Scott is working on an update.
Old Waldorf plugs died: PPG, Attack and D-Pole, no pass AUval.
For NI Massive I at first got an error message it couldn't find a resource file. After a Google search I ended up going into the System folder and change the first letter in one of Massive's resource files name from uppercase to lowercase or vice-versa, but apparently that also happened to folks on Leo on occasion. Looks like NI was sloppy in their lowercase/uppercase when referencing the file in the code, but once I knew that I fixed that in seconds. Works great now.
Other than Schwa/Stillwell, the only ones that broke completely for me are my FXpansion VST-wrapped plugs. Most of those ended up with dead GUIs, though they processed audio just fine. But of course you can't edit sh*t. Most weren't very important to me, they were all freebies. The VST-wrapped D16 Phoscyon works, but you can't access presets. Hoping they release that as AU soon, like their other plugs.
Softube work great, but the cursor for all plugs wiggles a bit when it's over the plug-in GUI. Not very hard, so it's a minor nuisance, and the controls remain responsive. I'll report that to Softube if it continues doing this in DP7.
Waves IR-L and IR-L lite GUI shakes like an earthquake as soon as you edit anything. Stops when you move the plug-in window a couple of times, and restarts shaking as soon as you edit again. Ditto for Supertap 2-tap. All other Waves work great. Now I never use IR anyway (use Altiverb 99% of the time) so I didn't care. Supertap 6-tap works great, so that's my new first call Waves delay.
BFD 1.5 is dead, crashes AUval. BFD2 works like a charm.
NI says you cannot at the moment install their plugs from scratch while in SL, but existing installs work great when the computer gets upgraded to SL with NI already installed. And yesterday's Battery 3.06 update installed just fine here.
Now here's a list of the plugs that so far are working like butter:
112dB redline reverb, all AAS, all Abbey Road, all AraldFX, all Arturia, all AudioDamage, Audioease Altiverb and Speakerphone, all Cakewalk Mac plugs, all CamelAudio, all CodeOperator (in fact *all* my remaining Pluggos work MUCH better than they used to) all D16 Group AUs (not their wrapped VSTs), all Daevlmakr pluggos (great stuff!), all DDMF, EW Play, all Expertsleepers (go to their website for what to do for Crossfade Loop Synth), Fabfilter One, BFD2, all MOTU (as we know apparently not yet Ethno, don't have that), all Mr. Alias (sick stuff), all NI (see note re. "Massive" above), Ohmforce Ohmicide and Frohmage, Breverb, PSP Nitro and PSP Stereopack, QuikQuak Fusionfield and Upstereo, reFuse Lowender, Elemental Audio Inspector XL, Softube with the above mentioned graphical hiccup, Sonalksis (compressors need to have a dummy sidechain input assigned to pass audio, that's a DP6 issue, but work no prob), all Sonic Charge (xcellent stuff), Sonnox TransMod, all Soundhack, all SoundToys, all Spectrasonics, the one single Massey AU he made, SugarBytes WOW, all TAL (gr8 stuff and free, unbelieveable), Sound Guy Backwards Machine, and yes, all Tritone Digital Pluggos (yay!), all U-He synths and effects (now that's sick stuff, amazing software written by a genius in Berlin), all URS (Saturation 2 is essential), Virsyn miniTera, and all Waves with the above mentioned exceptions, which sorta work but not really.
Now, just to make sure nobody gets hurt...

- before I did *any* of this I made not one but
two clones of my entire system drive. I also did all the plug-in updates and the DP update BEFORE installing SL. Then I did a
third clone of that. And then, and only THEN, did I install SnowLeo...
Hope this helps!