These mods aren't CF | UK friendly, if caught abusing them or attempting to overload the server [We've been detecting abnormal packets from such users recently.] you will be banned without appeal.
It is recommended to keep a seperate .jar for your modded minecraft.
I only ever use one inventory editor for Minecraft SSP, and it's impossible (as far as I know) to use in SMP (as it requires to load and save your MC save file every time). It cannot be used in-game, and thus won't have any stress on the server (nor work, for that matter - not that I've even bothered trying).
There are a lot of interesting mods out there (when I say interesting, I mean mostly those "non-cheat" and "non-hack" mods), but I don't use any of them because I like to keep my SSP as close to SMP as possible. Why? Because it's SMP I love, and I don't like getting use to one thing in SSP only to have to get re-used to something in SMP.
I've been playing a little bit of SSP myself lately. It's more of an exercise for me, and some prudent planning (seeing how it will look in-game if I decide to build something on the server).