With the current portable computing market being very strong and offering hundreds of choices from full laptops, to portable media stations, to ultra-portable PCs, to smart phones and PDAs, you really need to know what you're looking for prior to going out to purchase.
The current popular classifications of portable "smart" electronics allows everything to fall in to one or more of six categories: full laptop, thin-and-light laptop, UMPC, tablet PC, smart phone, or PDA.
Full laptops are the style notebook you're used to, they range in size and weight, but are generally much heavier and bulkier than the other options. They're also significantly more powerful, however, at a much higher power draw - which usually results in battery life of circa-four hours. Some laptops have dedicated graphics processors, however, most in the consumer price range do not - thus, gaming on laptops can be difficult and pricey.
The new "thin-and-light" style notebooks have caught on dramatically in the last few years. With the majority of the same features of the full laptopns, thin-and-lights usually sport 13- or 14-inch screens, light weight, and many energy conserving features to optimize battery life. These laptops also will not work well for gaming, but for business and web related work, will work amazingly.
UMPCs are a recent release from Microsoft, although, previously released as handtops - the handtops category quickly died out. UMPCs are usually small enough to fit in one hand, sport a variety of styles, usually a QWERTY keyboard, Windows XP or Tablet Edition operating system, low specifications, and generally low battery life. The most prominent UMPC on today's market is the OQO. These are usually very pricey, and the small screens make them rather unattractive for gaming.
Tablet PCs are an old invention, and usually look a lot like a piece of thick paper. The screens are touch sensitive, and the mouse is usually controlled with a stylus, rather than a mouse or touchpad. Specifications and battery life is frequently lower than usual in these, and prices are usually substantially higher. They are much smaller than full laptops, though much bigger than UMPCs.
Smart phones and PDAs are frequently classed together, since the main difference is the ability to connect to a PST (public switched telephone) network. PDAs are personal digital assistants, and usually don't feature a full operating system past simple functionality such as address book, calendar, and notetaking.