It all depends on the provider. If the provider can provide enough bandwidth for the concurrent access, should be no problem. Been using Maxis BB for a while. There this once, we had an off site meeting in Danga Bay, I noticed there was Maxis Center nearby so the signal was superbly strong. For killing the time, few of us start showing off our gadgets. Since I got friends wanted to share my broadband, I took out my MIFI, otherwise, my laptop is broadband ready without the use of MIFI. To cut the story short, there were 2 IPADs, 2 laptops and 1 PDA accessing the Internet via MIFI.

Verdict:
Since the connection was HSPA with speedtest between 5mbps - 15mbps. MIFI proven to be very helpful. Normal browsing, email reading, instant messaging, no lagging. Video streaming (Youtube) starts to lag if 3 devices playing Youtube video at the same time. We tested Celcom 5Gb, needless to say, we switched back to Maxis. The Maxis we used was only 1 hour pass using Hotlink prepaid.

PS. Not promoting Maxis just sharing experience.