I've been using a 510 for almost six weeks now (I'm one of those .......s who dropped analogs after nearly the first puff off a PV), and just received an eGo yesterday.
Yes, I got the eGo because of the fact that after about 150 of the 200 - 300 charge-cycles the standard 510 battery is rated for, they lose about half their vape-life. I was swapping my first two batteries (I got the 510/PCC kit from Cignot, on the wise and welcome recommendation from a couple friends) almost faster than they could charge after 5 weeks, so I decided to spend the money to quash my paranoia of being stuck w/out a PV during the day.
That being said, the "heart" of any PV is the atomizer, and the 510 atty produces IMHO more and better vapor of any other 3.X volt device, and I tried several before I bought even my first 510. Given the right platform, juice, and a little TLC, they are awesome producers and long-lasting. Especially for the price.
To answer your question: I got the eGo for work/random long trips.
But, at the same time I got the eGo, I also ordered more 510 attys (so now I'll have a total of 13, with 3 in use and 10 on reserve for whenever they start blowing... hasn't happened yet!), 3 more regular batteries, and a long battery for those occasions where I want longer battery life, but don't want the stubby "cigar" shape of the eGo, like a night on the town... or my upcoming wedding.
Yeah, a bunch of bucks... but from where I sit, having spent about $200 - $300 a month on analogs for the past several years, it's well worth it. And yes, outside of work, I still use the regular ol' 510 and probably will for quite a long time. It's a nice compromise between a super-mini "cigarette-sized" device, and a (somewhat) longer-lasting device that still retains the handling characteristics of an analog... and yet has other options like the Bartleby or eGo/Tornado if you want that too.
- Inspector Callahan