While I don't like internal locks in particular, I specifically don't like them on revolvers.
Why don't I like internal locks in general? Most of the prior replies have pretty well summed up my feelings on the matter: Decreased reliability, increased potential for something going wrong, eyesore, inhibits legit SD, etc. One other reason for not liking them is the rationale behind installing the infernal things in the first place. They are a sell-out to the anti's, nanny staters and assorted litigous scumbags -- nothing more than that. While I agree that it would be better to thave those assinine locks than to not have guns available at all, it would be even better to stand up to those infernal forces and tell them to go bugger off.
Why moreso on revolvers? It is more of a mindset than anything else. I am attracted to revolvers in general because of this aura of "old school" that is about them. They are not supposed to be up-to-date with all of the latest wiz-bangery. They are supposed to be "throwbacks" to an earlier age -- I cling to them because they worked well back then and still work just as well now, without all of the newer, fancier techno-whatever. Adding that extra bit of unneccessary complexity is an assault on that tried and true simplicity. It (the lock, not the revolver) becomes an abomination.