I currently work with 162 parts (most of them are sheet metal parts), and I experience some lags, but no hang ons. Its essential, that you use simplified parts to get things run smoothly. I have spoke with some people, that are using over 700 parts within one assembly without problems. My configuration is AMD Athlon 800 MHz, 512 Mb RAM, 40 Gb HD, And ASUS 6600 Graphics card. I noticed no problems SAVING and REBUILDING OR editing parts within large assemblies.