I have several clients that use Aweber and I am not impressed by their services. The last few months there has been unannounced downtime, the control panel can be a bit quirky, sign up confirmation can be slow and sometimes the javscript for forms stops working.
The most irritating part is the chat support...
"Hi, I am having some issues here"
"Everything seems to be working fine here, clear your cache, restart your browser, blah, blah, blah"
Since the last upgrades they did, the quality of service has gone downhill.
Like I said, not impressed.