I've noticed Blockchain Wallet freeze up after about 15-20 transactions in 30 minutes.
Bitcoin also has a tendency to lag up after ~400 transactions in 48 hours.
Multibit locks up after ~150 transactions in 24 hours.
Electrum is the one I've been messing with for a while and so far the worst thing is the seconds not showing up for the transaction time. It's frozen up a few times, but a simple switching of the server fixed that.
Sounds like you're running on slow hard drives, or your hard drive is having problems. I was playing with a custom SD Bot using stock bitcoind on my VPS (Raid 10 + 10k drives). Lag didn't start becoming an issue until the wallet hit ~250 megs with 10k+ transactions. Even then it normally wasn't bad. Although now I have it modified to send change back to the original address, which stops the wallet from bloating up so badly in the first place.