The latest version of the Intel Application Accelerator IDE drivers for i8xx series chipsets is quite good.
The largest gains are seen with Pentium 4 processors under Windows 2000. Gains of generally around 10% are seen with these drivers, although the improvement is less pronounced under Windows XP as Microsoft's IDE driver is also quite aggressively written.
I do not recommend using them under Windows 98(SE), and to a lesser extent, Windows ME.
They do occasionally cause problems for CDRWs as well, but this is improving with each revision of the IAAs.
Remember that you must install the Intel Chipset Inf drivers before installing the IAAs.