I rarely see people tying in with a single bowline, for the reason you give. I've been using a double bowline with a stopper knot (http://www.vdiffclimbing.com/double-bowline/) for many years now (well, at least outside of the climbing gym). I've never had an issue with the knot loosening when not under load. The usual complaint I hear from people about using it to tie-in is that it is harder for your partner to visually verify. The figure-8 follow-through is very easy to visually check.

ETA: The last person I saw tie-in with a single bowline was Christian Griffith (of Verve fame) using it to tie-back in after cleaning the anchors of a warm-up in the Ruckman Cave at Rifle Mountain Park. He also didn't secure the rope whe he untied to thread the anchors, choosing instead to just step on it. Not exactly a great example of anchor safety...