I have a rooted Samsung Galaxy Ace GT-S5830L with Android 2.3.4, with factory ROM. It works pretty well with most WEP/WPA2 wifi hotspots. When I try to connect to an open one, no matter the signal intensity, it connects for a couple of seconds then disconnects and keeps doing so. I can't state for a fact that this is only restricted to open hotspots but so far thats the pattern I have identified.
I have heard that Galaxy phones have some wireless issues but I'm not sure how to deal with mine.
This might be related to: Why Smartphone Disconnects From Certain Hotspots Sometimes?