They are good for a fair few things (I looked hard at things like OneNote and Evernote in the wiki role, but chose a wiki because of crosslinking), but the data is hard to extract from their formats.
You can cross-link in Evernote and OneNote. Also, Evernote has a great feature called Context which is activated if you pay for a subscription (worth it) that automatically shows you relevant notes based on your current note. Also, Evernote is a lot more portable than a Wiki so you can carry it around and search through all your notes (including inside PDFs and other documents, OCR and images).
