Find Highlight may need a cancel button

It made my computer unresponsive for about 10 seconds.

Out of curiosity, how many words do you have in your draft? I’ve seen extremely minor wait times (on order of microseconds) before, but never anything dramatic like multiple seconds. If your word-count is not especially high, there might be something else going on here. When was the last time you closed Scrivener? Has it been open for weeks on end? My computer will sometimes get slow if I leave it on for weeks, and sometimes applications themselves can get slow as well. For me this has been an issue with Leopard. Another question: has it ever happened consistently, or was it a one-time thing? It could be that your computer was in a sleep state, had to spin up a drive, scan a DVD, or respond to network latency—halting drive speed for a bit. If it doesn’t happen consistently, it just might have been a freak occurrence.