I've seen my Oregon freeze during start-up countless times. I was travelling with two micro-SD cards containing 2000 geocaches each, and switching them according to region. When I switch the cards, Oregon obviously goes through process of reading all those geocaches, which takes some time, and with 2000 caches in my experience freezes at least 50% of time. Some times, after freeze, when it's turned on, it freezes again. Other times, it will just boot quicky, but geocache database ends up incomplete/empty (and nothing short of removing micro SD card and inserting different one/master reset can force it to read the card again).
Once it gets throuph process of reading whole geocache database without freeze, it usually works flawlessly until card change, although there's one hurdle. For weird reasons, sometimes Oregon reads geocache database even when the card isn't changed (you can tell, because start up takes much longer then usuall), and again freezes at least 50% of the time when attempting this.
It seems to be realed to former Memory full issue. With firmware prior to 2.4, unit offten generated Memory Full message after changing card, and ended up with incomplete geocache database, but freezes were less common. With 2.4 or 2.5 firmware, Memory Full message is gone, but freezes happen instead.
Master reset always worked for me, and it hardly ever freezes right after master reset. But, having to master reset unit about 5 times a week kinda sucks. I hope to see some fix for this soon.