After many years of using a 3G stick for my notebook on my daily commute I've finally made the switch to Wi-Fi tethering, either to an Android smartphone or an Android tablet, whatever I carry on a particular day. For the moment, it seems more convenient as that 3G stick requires some extra space which is at a premium in trains.
That makes me wonder if 3G sticks will have a future or if their will be completely replaced by Wi-Fi tethering, even more so because a 3G stick needs a separate SIM card which is usually a hassle and which often costs extra money. The few megabytes I use during my daily commute can easily be absorbed by my smartphone plan that does not exclude tethering use.
Speed wise I have not seen a difference between a 3G stick and smartphone tethering. Over both connections I can easily reach speeds well over 6 MBit/s, depending of course on cellular signal quality. Sure, dual-carrier sticks can go far beyond this speed but LTE smartphones with tethering capabilities are now on the market, taking away this advantage as well.
I've also noticed interesting Wi-Fi power saving mechanisms. While the ping round trip delay times are quite normal when tethering to my smartphone, they are around 300ms when tethering to the tablet. However, when I transfer more data over the tablet than just the ping packets, round trip delay times are down to the usual 60 ms again during the transfer and return immediately to 300 ms afterwards. This rules out cellular power saving schemes like Cell-FACH and Cell-PCH which take a much longer time to get activated. No disadvantage but I was a bit surprised when I saw the 300ms for the first time and initially thought something was wrong.
One thing that is an advantage as much as a disadvantage is that the smartphone or tablet runs on a battery vs. the 3G stick that takes the power from the notebook. On the positive side my PC runs a lot longer on a charge. My Lenovo Thinkpad requires about 12 Watts without the stick and an additional 3-4 Watts with the stick (depending on the type of 3G stick). This cuts the operation time by at least one and a half hours.
On the negative side I have to remember to activate/deactivate the Wi-Fi hotspot option on my smartphone once I arrive at work or at home. I wonder when we'll see an option to switch off the Wi-Fi hotspot functionality after a configurable time when no clients are active anymore.I faintly remember of already having seen such an option in a device but it deactivated the hotspot immediately after the last client had left. Not good for my train scenario in which every now and then suspend the notebook for a minute by closing the lid to answer a call or to show my ticket.
But even when switching off the Wi-Fi hotspot functionality after use the smartphone probably doesn't last a full day when using it for other tings, too, as a Wi-Fi/3G bridge for an hour a day with frequent data transfers requires quite some power. The tablet's got an advantage here due to its much bigger battery.
Another downside of the tethering solution is that in other scenarios such as libraries or at Starbucks two power sockets are required, one for the PC and one for the smartphone/tablet. Usually one is lucky if there is even one socket available.
But tethering is often cheaper than having an extra SIM for a 3G dongle which is why I think most people will not mind the drawbacks in some situations.