Overall: Pretty good.
1. In spite of 3G theoretical bandwidth of 384 kbps, CBN XL bandwidth is limited to 64 kbps (that's kilo bit per second), which translated to 8 KBps (Kilo byte per second). In practice, it's around 6 to 7-ish KBps. But early on March, it was around 20KBps according to Sony Ericsson update manager.. I guess they cut it down.
2. The connection is pretty stable. Disconnect is rare even when your 3G modem moves around Jakarta while connected.. Maybe 1 out of ordinary disconnect every 2 days. That's excluding a what seems to be a pre-programmed disconnect every 24 hours period of connection. I guess it's their method to enforce the so called dynamic IP..
3. Sometimes it's difficult to start connection. When that happens, wait for a while and repeat. I give up trying to find the culprit (either from CBN or from XL). Some other time, you can connect but you can't resolve any website name. Reconnect until you're assigned to the correct DNS.
4. The latency seems higher compared to dial up. In short, the connection might take a while before responding to a request. For example, if you click a link, it might take a while before the modem start receiving data on the link.
Self-ping takes around 300ms to 400ms. That's above a healthy people average reaction. Consequently, I think real time online gaming is not feasible, but I haven't tested it yet..
5. For a quick reference, bluetooth 1.2 can sustain CBN XL bandwidth.
Edit 24 April 2008: It seems since 15th March 2008, Cyberindo reduce the bandwidth to a paltry 3KBytes/s. The lag is also unbearable. I guess they decide reduce the quality of this unlimited subscription service to make people move to their new service, which are volume based.
*sigh* I hate entity who don't have the guts to be frank..