I've worn quite a few mid-layers this winter, including the Patagonia Velocity and the Marmot Dri-Clime. Different garments, different strengths and weaknesses. You can read a review of the Dri-clime here: UKC Review.
The Velocity is essentially a fleece top. It has a zip neck, is very stretchy and has a smooth finish on the outside. It has a 'body hugging' fit, a fleecy feel on the inside and fairly snug fitting sleeves and cuffs.
I'm tall (6'2”) and thin, but usually wear a size large to accommodate my ape-length arms. I have the Patagonia Velocity in a medium and it fits just fine.
I've had the velocity now since December (3 months) and as is the stinky nature of winter climbing, I have worn it and washed it numerous times. I've used it as a base/mid-layer underneath my shells and I've also used it as a top layer for rock climbing and running.
The top isn't a heavy weight fleece, being only 274g, it is a lightweight mid-layer or even base layer. The main plus points in my opinion have been the incredibly good fit and the smooth outer finish.
The fit is indeed 'body-hugging'. What this means is a next to the skin feel, no flapping of material and no baggy bits. The sleeves are quite snug around the forearms, which means that the top doesn't ride up when switching shells or faffing with gloves. It may mean that if you have arms like Popeye, the top might not fit. Luckily I'm more Olive Oil myself...
The stretchy Polartec fabric is very comfortable and the smooth outer means that the top slides well underneath your shell. This kind of design feature can really make a difference, like when you're fully togged up and trying to execute some sort of Houdini-style Yoga move in a Scottish winter chimney.
The women's version has thumb loops in the wrists, which are quite a handy feature – but obviously us men are far too tough to need anything like that.
The top has lasted well so far, I think the tight fit helps reduce wear by making sure the fabric doesn't get caught on anything. After around 10 washes the outer is starting to look a tiny bit 'bobbly' in a few places, but basically the top has been put together extremely well.
It's not wind-proof, it's not water-proof and it won't make you breakfast in bed. It's a snug fitting, stretchy fleece top that comes in a variety of colours and sizes (and a women's specific shape too).