Proficiencies: All and often. Yes, I totally concur with the notion that everyone can basically trry anything, but those who have the training do it well. Going with that, it is still entirely in the GMs purview to say that there are things within the proficiencies that someone "untrained" could not or should not be able to attempt.
Conventions: On the D20 radio Downloads page (under the support tab) one of the available Downloads is "FULONGAMER's Guide to GenCon Mastery". It is assuredly also applicable to all smaller cons adjusted for scale.
If you are running adventures at a CON, then you definitely have to adapt the GM style and the adventure style to the Con atmosphere. Basically think of adventures generally in 4 hr blocks. If you are running long adventures, either upfront announce that in the event schedule (6hr - 8hr single sessions) or construct the adventure in defined segments, EXACTLY like the old classic AD&D Tournament Modules (A Series, S Series, U Series, GDQ Series). Pre-gens are usually the rule of the day and the evolutions from one block to the other are proofed against the in-and-out players, even more so if it is tiered advancement tournament rather than just a broken up timeline of a 12-18 hr "mega adventure".
If you are looking for the "more current" versions of 2E spells, of course you must reference the 4 volume set Wizards Spell Compendiums (1996)http://www.amazon.com/Wizards-Compendiu ... 901&sr=1-1
And the Priest's Spell Compendiumshttp://www.amazon.com/Priests-Compendiu ... 901&sr=1-2
And the Encyclopedia Magica (items)http://www.amazon.com/Encyclopedia-Magi ... 901&sr=1-3
DMVincent has seen these, over in the SoD boards, but they are creations of mine using the guidelines in the Complete Wizards Handbookviewtopic.php?p=70992#p70992
Death Knights: We had a gm decide that we were going to have an open-field charge battle against not one, but 9 Death Knights. 8 "regular" and 1 "Paragon" Death Knight. (this is what comes from letting the Cavalier think he's in charge)
As far as ME using them as a GM, the last time I did was as a result of the party in a dungeon using a reversed wish (unwittingly) to ressurect a recently deceased high level party member fighter. He sat up as a Death Knight and chaos ensued.