Badly designed - apart from the fact that the software has a poor user interface, opening the port required for access is a significant security risk. I guess Windows users are just used to compromised security ;-)
Too cumbersome - every time I try to use it I have to start by downloading an installing a new version of the client software. By that time, I've lost interest or the event I'm supposed to be attending is over.
Lack of imagination - that fact that almost every project feels it has to build a representation of the real world is a chronic indictment of the lack of imagination that Second Life represents. If I was training astronauts for a Mars mission, I might want to build a realistic representation of the environment they would be working in. I could replicate an English cathedral - but why bother? If I want to train students in genetics, do I need to build a laboratory with trees outside the window? Does a representation of surfing in Hawaii with palm trees make me more inclined to want to go surfing than a cold Cornish beach with the wind in my hair and the smell of the sea? Get real!
Cost - in case you haven't noticed, a public spending time bomb is about to decimate education. Stop wasting money on expensive strategies which are not supported by evidence of effectiveness or cost-effectiveness. Sub-contracting pedagogy by employing firms of developers to build "stuff" for you because you can't use the tools you are expecting students to use is about to become socially unacceptable.
Online identity - Far-sighted educators have been working with students choices of online identity. Second Life gets in the way. I want to spend my time teaching/learning, not fiddling about with a cartoon representations of myself, or worse, paying someone else to do it for me. I want to build my personal brand, use my own name online, not some dumb name Second Life picks for me. I also want to use my own image as avatar to build trust - a Futurama head in a jar is just fine as far as I'm concerned.
Data portability - in Second Life? Don't make me laugh. At least you don't have to waste money building walled gardens in SL - they've built it for you.
Sleaze - I had an "interesting" time choosing pictures to illustrate this post...
So what's good about Second Life?
I'm not against virtual environments - it's SL I have a problem with. There are many potential applications, the ones that particularly attract me being travel replacement and carbon footprint reduction. However, I don't feel that virtual environments are good conferencing tools - I don't need a 3D representation and the lighter touch of tools such as Eluminate and Skype are much more appropriate for this application.
Google Lively was a much more promising tool than Second Life - until Google pulled it. Simple embedding of Lively "rooms" into any HTML webpage meant content could be provided in a two-dimensional format, and communication surrounding the topic of that content could be made in the three-dimensional room without the need to enter a separate program. Nice.
Some of may gamer colleagues argue that World of Warcraft is a much better prospect for education than Second Life. Certainly the emergence of user-generated Guilds is an interesting model in an educational context.
So I'm pleased to be able to finish on a positive note. There is, above all else, one thing that Second Life is unsurpassed for. If you need to generate a large amount of cash from a naive grant-awarding body over-eager to jump on the Web 2.0 bandwagon, offer to build, for a preposterous amount of cash, a virtual representation of something that already exists in the real world but that no-one will ever use in SL. Something like, say, Belgium. You'll be quids in. Careers have been built on it.
If you want your say, you can leave a comment below, or join us at the Future of Technology in Education Conference 2009 via Twitter: #fote09