The mark-to-market, fair value debate is a rich one, with the two sides both having support. In principle, of course, mark to market is great -- market prices impound all relevant information, so they should be used in financial statements and in regulation as well. The issue today is not even how informative prices are (I could argue they are not) but how informative mark to model results are. Without knowing all the parameters that were used to fairly value assets, in the absence of relevant market prices, I think I might prefer just full disclosure of holdings and let me do the valuations (of course, we don't have full disclosure either, so we are really choosing from imperfect choices).
But nonetheless, my belief is that for banks, most securities and derivatives have been marked down to levels that are, at worst, not too much above any sense of true value. Thus, there is a tremendous upside for mark-ups once asset prices begin to rise (and they will). If we repeal mark to market now, banks will be able to take some write-ups, which will of course get reported as profits, just as the writedowns were taken as losses. If we don't repeal mark to market, I expect the gains will come a bit later, as valuation models won't change immediately. The total gains to be reported will be the same, but the timing may well be different. If one believes in some market psychology, I suppose that there could be a differential effect. I am not one to bet on such things, but I could see an argument for keeping mark to model for now and letting the writeups occur with a big bang all at once -- hopefully sometime soon. Since in principle I think mark to market is what we want, we might as well stick to our principles and hold out for what could be some massive writeups.