I'm having a similar issue, I get a message that storage is almost full. When I checked Usage (Settings-->General-->Usage) I see 0 MB of 13.7 GB is free. I deleted several apps (this was not an iCloud message) but the message keeps popping up (I have 437 MB free now). I tried a forced shutdown, but when the phone powers back on, it sits at the Apple screen. I'm going to try a restore once I get home, and hope that resolves things. One other symptom---everything on the phone is slow. When I press an app icon, it takes 5 seconds to open the folder, then another 5 seconds to bring up the app. Some apps display a blank screen, while others open, then force close. If this was a Windows POS, I'd think I have a virus. If a restore doesn't work, a trip to Verizon, and an upgrade to a 32 GB 4S may be in my future. Hope that doesn't reset 2 year commitment, because I was going to upgrade to an iPhone 5 in October. My message just started today and I haven't downloaded any new apps since Monday (I've been on iOS 5 since it came out, so this doesn't appear to be an iOS 5 issue).
I started having this exact same issues a couple days ago. It is wreaking havoc on my phone!
Nothing is performing correctly and no matter how much I delete, it doesn't last.
What is filling up that space on it's own???
Just tried your suggestion and it worked perfectly. I had a massive portion of my iphone taken up by OTHER when in fact I have very few apps, no photosor videos etc. Not sure what the OTHER was but what you suggested cleared most of it out. Thanks!