I have been using Delibar for more than two years and I never had a single issue with it. Since I am a Pinboard user I cannot comment on how the app performs with Delicious accounts, but Delibar in combination with Pinboard is just a joy to use - the app is fast, stable and pretty and the keyboard shortcuts are a godsend. Never having to use the mouse to interact with Delibar is worth the price alone for me ;)) The search is also remarkably fast and smart enough that I can find the item I'm looking for instantly.
I wonder if the problems with speed and chrashes, that the reviewer before me mentioned, have to do with the amount of bookmarks (I have around 2000), the multiple accounts or maybe with Delicious itself? Maybe there are differences between the Appstore and Non-Appstore versions (I use the Non-Appstore version)?
Whatever it is, it's a shame - because Delibar really is an awesome application and has always performed flawlessly for me. Also, the auto-completion of tags is instant in my case, like absolutely and totally instant.
I can highly recommend Delibar (at least for Pinboard users), but you might want to do some testing with the free version before you buy - it seems that there are some performance differences depending on your setup.