Tablets are great for content consumption, productivity, and light content creation. For heavy lifting, it's best to use a desktop or laptop. Only you can decide if you frequently need to do heavy lifting whilst away from your office or desktop. Here is my list:
1. Content consumption (tablet)
Music
Video
Movies
Streaming content
eBooks
Web browsing
Maps and Directions
Photos
Games
Social media (e.g. Facebook and Twitter)
2. Productivity and Light Content Creation (tablet)
Email
Messaging
Calendar
Contacts
Reminders
Notes
PDF Review and annotation (e.g Good reader)
Cloud files and document management (e.g. Dropbox)
Simple document creation and editing (Pages, Numbers, and Keynote)
Financial Tracking and e-banking (e.g. Mint)
Access work related databases (e.g. LogMeIn)
Light photo editing and management (e.g. iPhoto, Flickr)
Simple slideshow and movie creation (e.g. iMovie)
3. Moderate to Heavy Content Creation (laptop or desktop)
Writing long papers and reports (to some extent, this can done with a tablet + bluetooth keyboard)
Developing and editing moderately large or complex spreadsheets
Developing lengthy or complex presentations
Creating and manipulating databases and reports
Video and music editing and creation
When away from your office, if you mainly do stuff on lists 1&2, then a tablet should be fine and the iPad Air would be great. If you do a lot of stuff on list 3 when away from your office or desktop, then you need a laptop or you might want to wait for some kind of next generation device. I should mention that I know a fair number of professionals in responsible positions (CFO, Fund Manager, VP Manufacturing etc) that do real work and go iPad only when on business travel. They simply save the heavy lifting for back at the office.