It depends on what you're planning to do with the service. If you're just checking emails or browsing, it's may not be a big deal. If you're trying to use the SIP client and make voip calls over edge, I'm thinking it won't work too well.
Same thing with tethering,,, it works great on 3g.. slow as dialup on edge.
If you're used to 3g data and get good 3g service levels, you likely won't want to switch back to edge.