- File support is lacking. I know they can't support all file formats but Microsoft Office is not the only office suite out there. Outlook is also not the only e-mail client. Some support the OpenOffice.org suite, Firefox and Thunderbord exists but it's hit or miss.
- The interfaces are terrible. Google gives you something akin to their web page but it's too small for a big result set. Yahoo and Copernic do a bit better, with a grid-like list that is more compact and straightforward.
- Results are inconsistent. It's the typical problem of balance. Some return too few results. which means you miss what you are looking for. Others too many which nullifies the whole reason for the desktop search engine.
If only the interface was better...