I HAVE seen quite a few people doing things such as spamming torches in a protected area so as to gain xp, as well as openly mentioning do so in chat...
However.
This option is available to all sides, no?
With reference to Thabigdawgs opening statement on market crashing...with this option avaiable to all, true, there will be a LOT of enchanted stuff on the market. But I am reminded of my Economics lessons - a surplus of a set commodity means said commodity depreciates, becoming worth less.
Ie. 4 Picks enchanted, worth a total of say 200d.
In the same amount of time now = 20 picks enchanted, still worth the market total of 200d.
The items become worth less, in this case, by 80%.
The same total net profit overall is still the same, simply spread out.
'Swings and roundabouts' as the Playground developer used to say.
Certainly, if you begin banning people for this i know for a fact you're going to lose several notable members of your community, including a $300 donator.
There are other ways (ie mining netherrack with an efficiency pick, and old method of mine) but you'll end up with berks complaining and general bad feeling.
There are slightly more harmful glithces, for example the warworld portal glitch. Unsure if the plethora (love that word) of 'glitches' can be solved, but any way you do it you're going to upset a large community.
Not trying to be the devil's advocate, simply trying to see it from multiple sides.