Re: trem stability
It's usually due to the studs / adjustment screws (the posts that the knife edges pivot on), or the quality of the metal the trem is built from which determines how fast the knife edges and / or posts wear, etc. The tremolo springs also play a part in stability. These wear out after a while (it'll usually take a long time), and the sharpness of the knife edges also affects stability.
The best bridges you can buy are the top of the line Ibanez ones -- Edge, Edge Lo-Pro, and Edge Pro. There are some OK bridges on the cheaper models such as the Edge III (apparently it's an improvement over the Edge Pro II, etc), and of the other, non-Ibanez bridges, the Original Floyd Rose is good, plus the OFR's made by Schaller and Gotoh.
The cheap crap ones you should try and avoid are the Lo-TRS II and TRS in general, though some are better than others, such as the TRS 101.