Slow and unreliable with sqlite, but rock solid and amazing with postgres.
Today, every document I receive goes into my duplex ADF scanner to scan to a network share which is monitored by Paperless. Documents there are ingested and pre-tagged, waiting for me to review them in the inbox. Unlike other posters here, I find the tagging process extremely fast and easy. Granted, I didn't have to bring in thousands of documents to begin with but started from a clean slate.
What's more, development is incredibly fast-moving and really useful features are added all the time.